diff --git a/R/get_census_data.R b/R/get_census_data.R
index dd86516..1c1ebc2 100644
--- a/R/get_census_data.R
+++ b/R/get_census_data.R
@@ -4,8 +4,13 @@
 #' for specified state(s). Using this function to download Census data in advance 
 #' can save considerable time when running \code{predict_race} and \code{census_helper}.
 #' 
-#' @param key A required character object containing a valid Census API key, 
-#' which can be requested \href{https://api.census.gov/data/key_signup.html}{here}.
+#' @param key A character string containing a valid U.S. Census API key, 
+#'   which can be requested from the
+#'   [U.S. Census API key signup page](https://api.census.gov/data/key_signup.html).
+#'   
+#'   If [`NULL`], the default, attempts to find a census key stored in an
+#'   [environment variable][Sys.getenv] named `CENSUS_API_KEY`.
+#' 
 #' @param states which states to extract Census data for, e.g., \code{c("NJ", "NY")}.
 #' @param age A \code{TRUE}/\code{FALSE} object indicating whether to condition on 
 #'  age or not. If \code{FALSE} (default), function will return Pr(Geolocation | Race).
diff --git a/man/get_census_data.Rd b/man/get_census_data.Rd
index 012ecff..b2b7085 100644
--- a/man/get_census_data.Rd
+++ b/man/get_census_data.Rd
@@ -16,8 +16,12 @@ get_census_data(
 )
 }
 \arguments{
-\item{key}{A required character object containing a valid Census API key,
-which can be requested \href{https://api.census.gov/data/key_signup.html}{here}.}
+\item{key}{A character string containing a valid U.S. Census API key,
+which can be requested from the
+\href{https://api.census.gov/data/key_signup.html}{U.S. Census API key signup page}.
+
+If \code{\link{NULL}}, the default, attempts to find a census key stored in an
+\link[=Sys.getenv]{environment variable} named \code{CENSUS_API_KEY}.}
 
 \item{states}{which states to extract Census data for, e.g., \code{c("NJ", "NY")}.}