diff --git a/oauthenticator/google.py b/oauthenticator/google.py
index ed9cf4c0..581c810a 100644
--- a/oauthenticator/google.py
+++ b/oauthenticator/google.py
@@ -108,19 +108,28 @@ def _userdata_url_default(self):
         Unicode(),
         config=True,
         help="""
-        Restrict sign-in to a list of email domain names, such as
-        `["mycollege.edu"]`.
+        This config has two functions.
+
+        1. Restrict sign-in to a list of email domain names, such as
+           `["mycollege.edu"]` or `["college1.edu", "college2.edu"]`.
+        2. If a single domain is specified, the username will be stripped to exclude the `@domain` part.
 
         Note that users with email domains in this list must still be allowed
         via another config, such as `allow_all`, `allowed_users`, or
         `allowed_google_groups`.
+
+        ```{warning} Disruptive config changes
+        Changing this config either to or from having a single entry is a
+        disruptive change as the same Google user will get a new username,
+        either without or with a domain name included.
+        ```
         """,
     )
 
     @default('hosted_domain')
     def _hosted_domain_from_env(self):
         domains = []
-        for domain in os.environ.get('HOSTED_DOMAIN', '').split(';'):
+        for domain in os.environ.get('HOSTED_DOMAIN', '').lower().split(';'):
             if domain:
                 # check falsy to avoid trailing separators
                 # adding empty domains
@@ -162,11 +171,19 @@ async def update_auth_model(self, auth_model):
         configured and the user isn't part of `admin_users`. Note that leaving
         it at None makes users able to retain an admin status while setting it
         to False makes it be revoked.
+
+        Strips the domain from the username if `hosted_domain` is configured
+        with a single entry.
         """
         user_info = auth_model["auth_state"][self.user_auth_state_key]
         user_email = user_info["email"]
         user_domain = user_info["domain"] = user_email.split("@")[1].lower()
 
+        if len(self.hosted_domain) == 1 and self.hosted_domain[0] == user_domain:
+            # unambiguous domain, use only base name
+            username = user_email.split('@')[0]
+            auth_model["name"] = username
+
         user_groups = set()
         if self.allowed_google_groups or self.admin_google_groups:
             user_groups = user_info["google_groups"] = self._fetch_user_groups(
diff --git a/oauthenticator/tests/test_google.py b/oauthenticator/tests/test_google.py
index d9e24196..7a28388d 100644
--- a/oauthenticator/tests/test_google.py
+++ b/oauthenticator/tests/test_google.py
@@ -185,7 +185,12 @@ async def test_google(
         assert auth_model == None
 
 
-async def test_hosted_domain(google_client):
+async def test_hosted_domain_single_entry(google_client):
+    """
+    Tests that sign in is restricted to the listed domain and that the username
+    represents the part before the `@domain.com` as expected when hosted_domain
+    contains a single entry.
+    """
     c = Config()
     c.GoogleOAuthenticator.hosted_domain = ["In-Hosted-Domain.com"]
     c.GoogleOAuthenticator.allow_all = True
@@ -195,6 +200,40 @@ async def test_hosted_domain(google_client):
     handler = google_client.handler_for_user(handled_user_model)
     auth_model = await authenticator.get_authenticated_user(handler, None)
     assert auth_model
+    assert auth_model["name"] == "user1"
+
+    handled_user_model = user_model("user1@not-in-hosted-domain.com")
+    handler = google_client.handler_for_user(handled_user_model)
+    with raises(HTTPError) as exc:
+        await authenticator.get_authenticated_user(handler, None)
+    assert exc.value.status_code == 403
+
+
+async def test_hosted_domain_multiple_entries(google_client):
+    """
+    Tests that sign in is restricted to the listed domains and that the username
+    represents the full email as expected when hosted_domain contains multiple
+    entries.
+    """
+    c = Config()
+    c.GoogleOAuthenticator.hosted_domain = [
+        "In-Hosted-Domain1.com",
+        "In-Hosted-Domain2.com",
+    ]
+    c.GoogleOAuthenticator.allow_all = True
+    authenticator = GoogleOAuthenticator(config=c)
+
+    handled_user_model = user_model("user1@iN-hosteD-domaiN1.com")
+    handler = google_client.handler_for_user(handled_user_model)
+    auth_model = await authenticator.get_authenticated_user(handler, None)
+    assert auth_model
+    assert auth_model["name"] == "user1@in-hosted-domain1.com"
+
+    handled_user_model = user_model("user2@iN-hosteD-domaiN2.com")
+    handler = google_client.handler_for_user(handled_user_model)
+    auth_model = await authenticator.get_authenticated_user(handler, None)
+    assert auth_model
+    assert auth_model["name"] == "user2@in-hosted-domain2.com"
 
     handled_user_model = user_model("user1@not-in-hosted-domain.com")
     handler = google_client.handler_for_user(handled_user_model)