diff --git a/moto/iot/models.py b/moto/iot/models.py
index 258a387fe..4a7d43239 100644
--- a/moto/iot/models.py
+++ b/moto/iot/models.py
@@ -924,8 +924,12 @@ class IoTBackend(BaseBackend):
                 + thing_group_name
                 + " when there are still child groups attached to it"
             )
-        thing_group = self.describe_thing_group(thing_group_name)
-        del self.thing_groups[thing_group.arn]
+        try:
+            thing_group = self.describe_thing_group(thing_group_name)
+            del self.thing_groups[thing_group.arn]
+        except ResourceNotFoundException:
+            # AWS returns success even if the thing group does not exist.
+            pass
 
     def list_thing_groups(self, parent_group, name_prefix_filter, recursive):
         if recursive is None:
diff --git a/tests/test_iot/test_iot.py b/tests/test_iot/test_iot.py
index 7a04cdc16..e80a12a0f 100644
--- a/tests/test_iot/test_iot.py
+++ b/tests/test_iot/test_iot.py
@@ -1038,11 +1038,15 @@ def test_delete_thing_group():
     res.should.have.key("thingGroups").which.should.have.length_of(1)
     res["thingGroups"].should_not.have.key(group_name_2a)
 
-    # now that there is no child group, we can delete the previus group safely
+    # now that there is no child group, we can delete the previous group safely
     client.delete_thing_group(thingGroupName=group_name_1a)
     res = client.list_thing_groups()
     res.should.have.key("thingGroups").which.should.have.length_of(0)
 
+    # Deleting an invalid thing group does not raise an error.
+    res = client.delete_thing_group(thingGroupName="non-existent-group-name")
+    res["ResponseMetadata"]["HTTPStatusCode"].should.equal(200)
+
 
 @mock_iot
 def test_describe_thing_group_metadata_hierarchy():