diff --git a/_delphi_utils_python/delphi_utils/geomap.py b/_delphi_utils_python/delphi_utils/geomap.py
index 65885ffea..b3fe682a1 100644
--- a/_delphi_utils_python/delphi_utils/geomap.py
+++ b/_delphi_utils_python/delphi_utils/geomap.py
@@ -392,17 +392,17 @@ def replace_geocode(
         df = df.groupby([date_col, new_col]).sum().reset_index()
         return df
 
-    def add_population_column(self, geocode_type, data=None, geocode_col=None, dropna=True):
+    def add_population_column(self, data, geocode_type, geocode_col=None, dropna=True):
         """
         Appends a population column to a dataframe, based on the FIPS or ZIP code. If no
         dataframe is provided, the full crosswalk from geocode to population is returned.
 
         Parameters
         ---------
-        geocode_type: {"fips", "zip"}
-            The type of the geocode contained in geocode_col.
         data: pd.DataFrame
             The dataframe with a FIPS code column.
+        geocode_type: {"fips", "zip"}
+            The type of the geocode contained in geocode_col.
         geocode_col: str, default None
             The name of the column containing the geocodes. If None, uses the geocode_type
             as the name.
@@ -413,6 +413,7 @@ def add_population_column(self, geocode_type, data=None, geocode_col=None, dropn
             A dataframe with a population column appended.
         """
         geocode_col = geocode_type if geocode_col is None else geocode_col
+        data = data.copy()
 
         if geocode_type not in ["fips", "zip"]:
             raise ValueError(
@@ -422,15 +423,12 @@ def add_population_column(self, geocode_type, data=None, geocode_col=None, dropn
 
         pop_df = self._load_crosswalk(from_code=geocode_type, to_code="pop")
 
-        if data is None:
-            return pop_df.rename(columns={"pop": "population"})
-
         if not is_string_dtype(data[geocode_col]):
             data[geocode_col] = data[geocode_col].astype(str).str.zfill(5)
 
-        merge_type = "left" if dropna else "inner"
+        merge_type = "inner" if dropna else "left"
         data_with_pop = (
-            data.copy()
+            data
             .merge(pop_df, left_on=geocode_col, right_on=geocode_type, how=merge_type)
             .rename(columns={"pop": "population"})
         )
diff --git a/_delphi_utils_python/tests/test_geomap.py b/_delphi_utils_python/tests/test_geomap.py
index b756d1618..fca26b8ea 100644
--- a/_delphi_utils_python/tests/test_geomap.py
+++ b/_delphi_utils_python/tests/test_geomap.py
@@ -277,14 +277,12 @@ def test_zip_to_state_id(self):
 
     def test_add_population_column(self):
         gmpr = GeoMapper()
-        new_data = gmpr.add_population_column("fips", self.fips_data_3)
+        new_data = gmpr.add_population_column(self.fips_data_3, "fips")
         assert new_data["population"].sum() == 274963
-        new_data = gmpr.add_population_column("zip", self.zip_data)
+        new_data = gmpr.add_population_column(self.zip_data, "zip")
         assert new_data["population"].sum() == 274902
         with pytest.raises(ValueError):
-            new_data = gmpr.add_population_column("hrr", self.zip_data)
-        pop_df = gmpr.add_population_column("fips")
-        assert pop_df.shape == (3274, 2)
+            new_data = gmpr.add_population_column(self.zip_data, "hrr")
 
     def test_add_geocode(self):
         gmpr = GeoMapper()
diff --git a/jhu/delphi_jhu/pull.py b/jhu/delphi_jhu/pull.py
index 0330db62b..849c1f98a 100644
--- a/jhu/delphi_jhu/pull.py
+++ b/jhu/delphi_jhu/pull.py
@@ -101,7 +101,7 @@ def pull_jhu_data(base_url: str, metric: str, gmpr: GeoMapper) -> pd.DataFrame:
     )
 
     # Merge in population, set population as NAN for fake fips
-    df = gmpr.add_population_column("fips", df)
+    df = gmpr.add_population_column(df, "fips")
 
     df = create_diffs_column(df)