diff --git a/R-packages/covidcast/NEWS.md b/R-packages/covidcast/NEWS.md
index 76781ae7..7fcf31ad 100644
--- a/R-packages/covidcast/NEWS.md
+++ b/R-packages/covidcast/NEWS.md
@@ -8,6 +8,15 @@ Released TODO DATE.
   filter data frames with multiple issues of each observation, obtaining only
   the latest or earliest issue of each.
 
+- `covidcast_signal()` now batches requests, so that many days of data can be
+  fetched in one API call. This dramatically improves the speed of fetching
+  state-, MSA-, and HRR-level data, since many days of data can be fetched in
+  one API call. County-level signals, such as cases and deaths, may still
+  require one API call per day, since the API's row limit is only slightly
+  larger than the number of counties in the United States.
+
+- `covidcast_signal()` now fetches data from the API server in CSV format,
+  rather than JSON, which requires less bandwidth and parsing.
 
 # covidcast 0.3.1
 
diff --git a/R-packages/covidcast/R/covidcast.R b/R-packages/covidcast/R/covidcast.R
index 79817c29..ebdc1e4d 100644
--- a/R-packages/covidcast/R/covidcast.R
+++ b/R-packages/covidcast/R/covidcast.R
@@ -429,15 +429,15 @@ covidcast_signals <- function(data_source, signal,
 #'
 #' @export
 covidcast_meta <- function() {
-  meta <- .request(list(source='covidcast_meta', cached="true"))
+  meta <- .request(
+    list(source = "covidcast_meta",
+         format = "csv"))
 
-  if (meta$message != "success") {
-    abort(paste0("Failed to obtain metadata: ", meta$message, "."),
-          err_msg = meta$message,
-          class = "covidcast_meta_fetch_failed")
+  if (nchar(meta) == 0) {
+    abort("Failed to obtain metadata", class = "covidcast_meta_fetch_failed")
   }
 
-  meta <- meta$epidata %>%
+  meta <- read.csv(textConnection(meta), stringsAsFactors = FALSE) %>%
     dplyr::mutate(min_time = api_to_date(.data$min_time),
                   max_time = api_to_date(.data$max_time),
                   max_issue = api_to_date(.data$max_issue))
@@ -560,14 +560,14 @@ covidcast_days <- function(data_source, signal, start_day, end_day, geo_type,
 
   # The API limits the number of rows that can be returned at once, so we query
   # in batches.
-  for (i in seq(1, num_batches)) {
+  for (i in seq_len(num_batches)) {
     start_offset <- (i - 1) * max_days_at_time
     end_offset <- min(i * max_days_at_time, ndays) - 1
     query_start_day <- start_day + start_offset
     query_end_day <- start_day + end_offset
 
     time_values <- date_to_string(days[(start_offset + 1):(end_offset + 1)])
-    dat[[i]] <- covidcast(data_source = data_source,
+    response <- covidcast(data_source = data_source,
                           signal = signal,
                           time_type = "day",
                           geo_type = geo_type,
@@ -576,22 +576,37 @@ covidcast_days <- function(data_source, signal, start_day, end_day, geo_type,
                           as_of = as_of,
                           issues = issues,
                           lag = lag)
+
+    if (is.null(response)) {
+      warn(paste0("Fetching ", signal, " from ", data_source, " for ",
+                  query_start_day, " to ", query_end_day,
+                  " in geography '", geo_value, "': no results"),
+           data_source = data_source,
+           signal = signal,
+           start_day = query_start_day,
+           end_day = query_end_day,
+           geo_value = geo_value,
+           class = "covidcast_fetch_failed")
+
+      next
+    }
+
+    dat[[i]] <- response
+
     summary <- sprintf(
-      "Fetched day %s to %s: %s, %s, num_entries = %s",
+      "Fetched day %s to %s: num_entries = %s",
       query_start_day,
       query_end_day,
-      dat[[i]]$result,
-      dat[[i]]$message,
-      nrow(dat[[i]]$epidata)
-    )
+      nrow(response))
+
     if (length(summary) != 0) {
       message(summary)
     }
-    if (dat[[i]]$message == "success") {
+
+    if (nrow(response) > 0) {
       desired_geos <- tolower(unique(geo_value))
 
-      returned_epidata <- dat[[i]]$epidata
-      returned_geo_array <- returned_epidata %>%
+      returned_geo_array <- response %>%
         dplyr::select(geo_value, time_value) %>%
         dplyr::group_by(time_value) %>%
         dplyr::summarize(geo_value = list(geo_value))
@@ -607,10 +622,10 @@ covidcast_days <- function(data_source, signal, start_day, end_day, geo_type,
              signal = signal,
              day = missing_dates,
              geo_value = geo_value,
-             api_msg = dat[[i]]$message,
-             class = "covidcast_missing_geo_values"
+             class = "covidcast_missing_time_values"
         )
       }
+
       if (!identical("*", geo_value)) {
         missing_geo_array <- returned_geo_array[
           lapply(returned_geo_array$geo_value, length) < length(desired_geos), ]
@@ -626,26 +641,13 @@ covidcast_days <- function(data_source, signal, start_day, end_day, geo_type,
                signal = signal,
                day = api_to_date(missing_geo_array$time_value),
                geo_value = geo_value,
-               api_msg = dat[[i]]$message,
                class = "covidcast_missing_geo_values")
         }
       }
-    } else {
-      warn(paste0("Fetching ", signal, " from ", data_source, " for ",
-                  query_start_day, " to ", query_end_day, " in geography '",
-                  geo_value, "': ", dat[[i]]$message),
-           data_source = data_source,
-           signal = signal,
-           start_day = query_start_day,
-           end_day = query_end_day,
-           geo_value = geo_value,
-           api_msg = dat[[i]]$message,
-           class = "covidcast_fetch_failed")
     }
   }
 
   df <- dat %>%
-    purrr::map("epidata") %>% # just want $epidata part
     purrr::map(purrr::compact) %>% # remove the list elements that are NULL
     dplyr::bind_rows() # make this into a data frame
 
@@ -681,7 +683,7 @@ geo_warning_message <- function(row, desired_geos) {
 covidcast <- function(data_source, signal, time_type, geo_type, time_values,
                       geo_value, as_of, issues, lag) {
   # Check parameters
-  if(missing(data_source) || missing(signal) || missing(time_type) ||
+  if (missing(data_source) || missing(signal) || missing(time_type) ||
        missing(geo_type) || missing(time_values) || missing(geo_value)) {
     stop("`data_source`, `signal`, `time_type`, `geo_type`, `time_values`, ",
          "and `geo_value` are all required.")
@@ -689,14 +691,16 @@ covidcast <- function(data_source, signal, time_type, geo_type, time_values,
 
   # Set up request
   params <- list(
-    source = 'covidcast',
+    source = "covidcast",
     data_source = data_source,
     signal = signal,
     time_type = time_type,
     geo_type = geo_type,
     time_values = .list(time_values),
-    geo_value = geo_value
+    geo_value = geo_value,
+    format = "csv"
   )
+
   if (length(params$geo_value) > 1) {
     params$geo_values <- paste0(params$geo_value, collapse = ",") #convert to string
     params$geo_value <- NULL
@@ -721,8 +725,19 @@ covidcast <- function(data_source, signal, time_type, geo_type, time_values,
     params$lag <- lag
   }
 
-  # Make the API call
-  return(.request(params))
+  # Make the API call. If the API returns a non-200 status code, indicating e.g.
+  # a database error, .request() raises an error. It returns an empty string if
+  # there are no results for our query.
+  response <- .request(params)
+  if (nchar(response) == 0) {
+    # empty if no results
+    return(NULL)
+  }
+
+  # geo_value must be read as character so FIPS codes are returned as character,
+  # not numbers (with leading 0s potentially removed)
+  return(read.csv(textConnection(response), stringsAsFactors = FALSE,
+                  colClasses = c("geo_value" = "character")))
 }
 
 # Helper function to cast values and/or ranges to strings
@@ -751,8 +766,8 @@ covidcast <- function(data_source, signal, time_type, geo_type, time_values,
 
   httr::stop_for_status(response, task = "fetch data from API")
 
-  return(jsonlite::fromJSON(httr::content(response, as = "text",
-                                          encoding = "utf-8")))
+  return(httr::content(response, as = "text",
+                       encoding = "utf-8"))
 }
 
 # This is the date format expected by the API
diff --git a/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-1d9b5c.csv b/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-1d9b5c.csv
new file mode 100644
index 00000000..be57bbb1
--- /dev/null
+++ b/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-1d9b5c.csv
@@ -0,0 +1,2 @@
+geo_value,signal,time_value,issue,lag,value,stderr,sample_size
+01000,bar-not-found,20200101,20200102,1,1.0,0.1,2.0
diff --git a/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-3e1dc3.csv b/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-3e1dc3.csv
new file mode 100644
index 00000000..ee6523be
--- /dev/null
+++ b/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-3e1dc3.csv
@@ -0,0 +1,3 @@
+signal,geo_value,value,time_value,issue,lag,sample_size,stderr
+bar,pa,1,20200101,20200101,0,1,1
+bar,tx,1,20200101,20200101,0,1,1
diff --git a/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-64a69c.json b/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-64a69c.json
deleted file mode 100644
index ea92a725..00000000
--- a/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-64a69c.json
+++ /dev/null
@@ -1,26 +0,0 @@
-{
-  "result": 1,
-  "message": "success",
-  "epidata": [
-    {
-      "signal": "bar",
-      "geo_value": "pa",
-      "value": 1,
-      "time_value": "20200101",
-      "issue": "20200101",
-      "lag": 0,
-      "sample_size": 1,
-      "stderr": 1
-    },
-    {
-      "signal": "bar",
-      "geo_value": "tx",
-      "value": 1,
-      "time_value": "20200101",
-      "issue": "20200101",
-      "lag": 0,
-      "sample_size": 1,
-      "stderr": 1
-    }
-  ]
-}
diff --git a/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-6a5814.json b/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-6a5814.json
deleted file mode 100644
index ea92a725..00000000
--- a/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-6a5814.json
+++ /dev/null
@@ -1,26 +0,0 @@
-{
-  "result": 1,
-  "message": "success",
-  "epidata": [
-    {
-      "signal": "bar",
-      "geo_value": "pa",
-      "value": 1,
-      "time_value": "20200101",
-      "issue": "20200101",
-      "lag": 0,
-      "sample_size": 1,
-      "stderr": 1
-    },
-    {
-      "signal": "bar",
-      "geo_value": "tx",
-      "value": 1,
-      "time_value": "20200101",
-      "issue": "20200101",
-      "lag": 0,
-      "sample_size": 1,
-      "stderr": 1
-    }
-  ]
-}
diff --git a/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-96f6a5.json b/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-96f6a5.json
deleted file mode 100644
index c6adc102..00000000
--- a/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-96f6a5.json
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  "result": -2,
-  "message": "no results"
-}
diff --git a/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-b6e478.csv b/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-b6e478.csv
new file mode 100644
index 00000000..e69de29b
diff --git a/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-cb89ad.json b/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-cb89ad.json
deleted file mode 100644
index f0bf49d9..00000000
--- a/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-cb89ad.json
+++ /dev/null
@@ -1,17 +0,0 @@
-{
-  "message": "success",
-  "result": 1,
-  "epidata": [
-    {
-      "geo_value": "01000",
-      "signal": "bar-not-found",
-      "time_value": 20200101,
-      "direction": null,
-      "issue": 20200102,
-      "lag": 1,
-      "value": 1.0,
-      "stderr": 0.1,
-      "sample_size": 2.0
-    }
-  ]
-}
diff --git a/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-d2e163.json b/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-d2e163.json
deleted file mode 100644
index 7805d705..00000000
--- a/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-d2e163.json
+++ /dev/null
@@ -1,30 +0,0 @@
-{
-  "message": "success",
-  "result": 1,
-  "epidata": [
-    {
-      "data_source": "foo",
-      "signal": "bar",
-      "min_time": 20200101,
-      "max_time": 20200102,
-      "max_issue": 20200404,
-      "min_value": 0,
-      "max_value": 10,
-      "num_locations": 100,
-      "time_type": "day",
-      "geo_type": "county"
-    },
-    {
-      "data_source": "foo",
-      "signal": "bar2",
-      "min_time": 20201002,
-      "max_time": 20201003,
-      "max_issue": 20201101,
-      "num_locations": 100,
-      "min_value": 0,
-      "max_value": 10,
-      "time_type": "day",
-      "geo_type": "county"
-    }
-  ]
-}
diff --git a/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-d707dc.csv b/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-d707dc.csv
new file mode 100644
index 00000000..e69de29b
diff --git a/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-da6974.json b/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-da6974.json
deleted file mode 100644
index c6adc102..00000000
--- a/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-da6974.json
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  "result": -2,
-  "message": "no results"
-}
diff --git a/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-dd024f.csv b/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-dd024f.csv
new file mode 100644
index 00000000..27fa487a
--- /dev/null
+++ b/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-dd024f.csv
@@ -0,0 +1,3 @@
+data_source,signal,time_type,geo_type,min_time,max_time,min_value,max_value,num_locations,max_issue
+foo,bar,day,county,20200101,20200102,0,10,100,20200404
+foo,bar2,day,county,20201002,20201003,0,10,100,20201101
diff --git a/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-f666a2.csv b/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-f666a2.csv
new file mode 100644
index 00000000..ee6523be
--- /dev/null
+++ b/R-packages/covidcast/tests/testthat/api.covidcast.cmu.edu/epidata/api.php-f666a2.csv
@@ -0,0 +1,3 @@
+signal,geo_value,value,time_value,issue,lag,sample_size,stderr
+bar,pa,1,20200101,20200101,0,1,1
+bar,tx,1,20200101,20200101,0,1,1
diff --git a/R-packages/covidcast/tests/testthat/test-covidcast.R b/R-packages/covidcast/tests/testthat/test-covidcast.R
index 9f1961a3..46b8c70b 100644
--- a/R-packages/covidcast/tests/testthat/test-covidcast.R
+++ b/R-packages/covidcast/tests/testthat/test-covidcast.R
@@ -13,8 +13,10 @@ library(dplyr)
 # types of errors.
 #
 # 2. Once you've written a test, it can be difficult to find the file storing
-# the JSON needed for that test. We hence store the filename in comments
-# adjacent to every call.
+# the JSON or CSV needed for that test. We hence store the filename in comments
+# adjacent to every call. (Note that we request CSVs from the API for
+# covidcast_signal, and httptest suggests filenames ending in .json by default.
+# You can use .csv instead and httptest will correctly locate those files.)
 #
 # 3. covidcast_signal() calls covidcast_meta() unconditionally. We hence need a
 # single meta file that suffices for all tests that call covidcast_signal().
@@ -38,20 +40,20 @@ library(dplyr)
 
 with_mock_api({
   test_that("covidcast_meta formats result correctly", {
-    # api.php-d2e163.json
+    # api.php-dd024f.csv
     expect_equal(covidcast_meta(),
                  structure(
                    data.frame(
                      data_source = "foo",
                      signal = c("bar", "bar2"),
+                     time_type = "day",
+                     geo_type = "county",
                      min_time = as.Date(c("2020-01-01", "2020-10-02")),
                      max_time = as.Date(c("2020-01-02", "2020-10-03")),
-                     max_issue = as.Date(c("2020-04-04", "2020-11-01")),
                      min_value = 0,
                      max_value = 10,
                      num_locations = 100,
-                     time_type = "day",
-                     geo_type = "county"
+                     max_issue = as.Date(c("2020-04-04", "2020-11-01"))
                    ),
                    class = c("covidcast_meta", "data.frame")
                  ))
@@ -59,8 +61,7 @@ with_mock_api({
 })
 
 test_that("covidcast_meta raises error when API signals one", {
-  stub(covidcast_meta, ".request",
-       list(message = "argle-bargle"))
+  stub(covidcast_meta, ".request", "")
 
   expect_error(covidcast_meta(),
                class = "covidcast_meta_fetch_failed")
@@ -69,13 +70,13 @@ test_that("covidcast_meta raises error when API signals one", {
 with_mock_api({
   ## covidcast_signal() tests
   test_that("covidcast_signal warns when requested geo_values are unavailable", {
-    # api.php-6a5814.json
+    # api.php-3e1dc3.csv
     expect_warning(covidcast_signal("foo", "bar", "2020-01-01", "2020-01-01",
                                     geo_values = c("pa", "tx", "DUCKS")),
                    class = "covidcast_missing_geo_values")
 
     # ...but not when they *are* available.
-    # api.php-64a69c.json
+    # api.php-f666a2.csv
     expect_silent(suppressMessages(
       covidcast_signal("foo", "bar", "2020-01-01", "2020-01-01",
                        geo_values = c("pa", "tx"))))
@@ -83,12 +84,12 @@ with_mock_api({
 
   test_that("covidcast_signal warns when requested dates are unavailable", {
     # with geo_values = "*".
-    # api.php-96f6a5.json
+    # api.php-b6e478.csv
     expect_warning(covidcast_signal("foo", "bar", "2020-01-02", "2020-01-02"),
                    class = "covidcast_fetch_failed")
 
     # and with geo_values = "pa"
-    # api.php-da6974.json
+    # api.php-d707dc.csv
     expect_warning(covidcast_signal("foo", "bar", "2020-01-02", "2020-01-02",
                                     geo_values = "pa"),
                    class = "covidcast_fetch_failed")
@@ -101,7 +102,7 @@ with_mock_api({
 
   test_that("covidcast_signal works for signals with no meta", {
     # when no meta is available, we must provide start_day and end_day.
-    # api.php-cb89ad.json
+    # api.php-1d9b5c.csv
     expect_equal(
       covidcast_signal("foo", "bar-not-found",
                        "2020-01-01", "2020-01-01"),
@@ -123,7 +124,7 @@ with_mock_api({
   })
 
   test_that("covidcast_signal stops when end_day < start_day", {
-    # reusing api.php-da6974.json
+    # reusing api.php-dd024f.csv for metadata
     expect_error(covidcast_signal("foo", "bar", "2020-01-02", "2020-01-01"))
   })
 
@@ -139,7 +140,7 @@ with_mock_api({
 
 test_that("covidcast_days does not treat \"*\" as a missing geo_value", {
   stub(covidcast_days, "covidcast",
-       list(message = "success", epidata = data.frame(
+       data.frame(
          geo_value = c("geoa", "geob"),
          signal = "signal",
          time_value = c(20201030, 20201031),
@@ -149,7 +150,8 @@ test_that("covidcast_days does not treat \"*\" as a missing geo_value", {
          value = 3,
          stderr = NA,
          sample_size = NA
-       ), result = 1))
+       ))
+
   # Expect no warning
   expect_warning(
     covidcast_days(
@@ -168,7 +170,7 @@ test_that("covidcast_days does not treat \"*\" as a missing geo_value", {
 
 test_that("covidcast_days does not raise warnings for full response", {
   stub(covidcast_days, "covidcast",
-       list(message = "success", epidata = data.frame(
+       data.frame(
          geo_value = c("geoa"),
          signal = "signal",
          time_value = c(20201030, 20201031),
@@ -178,7 +180,8 @@ test_that("covidcast_days does not raise warnings for full response", {
          value = 3,
          stderr = NA,
          sample_size = NA
-       ), result = 1))
+       ))
+
   # Expect no warning
   expect_warning(
     covidcast_days(
@@ -196,19 +199,22 @@ test_that("covidcast_days does not raise warnings for full response", {
 })
 
 test_that("covidcast_days batches calls to covidcast", {
-  covidcast_returns <- rep(list(list(message = "success", epidata = data.frame(
-    geo_value = c("geoa"),
-    signal = "signal",
-    time_value = rep(NA, 3),
-    direction = NA,
-    issue = as.Date("2020-11-04"),
-    lag = 2,
-    value = 3,
-    stderr = NA,
-    sample_size = NA
-  ), result = 1)), 10)
-  covidcast_returns[[1]]$epidata$time_value <- 20101001:20101003
-  covidcast_returns[[2]]$epidata$time_value <- 20101004:20101006
+  covidcast_returns <- rep(
+    list(
+      data.frame(
+        geo_value = c("geoa"),
+        signal = "signal",
+        time_value = rep(NA, 3),
+        direction = NA,
+        issue = as.Date("2020-11-04"),
+        lag = 2,
+        value = 3,
+        stderr = NA,
+        sample_size = NA
+      )),
+    10)
+  covidcast_returns[[1]]$time_value <- 20101001:20101003
+  covidcast_returns[[2]]$time_value <- 20101004:20101006
 
   m <- mock(covidcast_returns[[1]], covidcast_returns[[2]])
   stub(covidcast_days, "covidcast", m)
diff --git a/R-packages/covidcast/vignettes/correlation-utils.Rmd b/R-packages/covidcast/vignettes/correlation-utils.Rmd
index 2ca9e3c2..80106e96 100644
--- a/R-packages/covidcast/vignettes/correlation-utils.Rmd
+++ b/R-packages/covidcast/vignettes/correlation-utils.Rmd
@@ -147,6 +147,8 @@ we can plot these correlations in space as a choropleth map, using
 
 ```{r, fig.width = 10, fig.height = 8}
 # Set a bunch of fields so that the data frame knows how to plot itself
+df_cor2$data_source <- "cor"
+df_cor2$signal <- "cor"
 df_cor2$time_value <- start_day
 df_cor2$issue <- start_day
 attributes(df_cor2)$metadata$geo_type <- "county"