- September 1, 1978:
- September 2, 1978: (The end of a storyline about Garfield going on a diet.)
- September 3, 1978:
- September 4, 1978:
- September 5, 1978: (Garfield is bathed for the first time. The comic is adapted in The Garfield Movie.)
- September 6, 1978: (This comic is featured in The Garfield Movie.)
- September 7, 1978:
- September 8, 1978:
- September 9, 1978: (The first strip that does not feature Garfield.)
- September 10, 1978:
- September 11, 1978:
- September 12, 1978:
- September 13, 1978:
- September 14, 1978:
- September 15, 1978:
- September 16, 1978:
- September 17, 1978: (The sixth panel is animated in Garfield on the Town.)
- September 18, 1978: (Garfield expresses his dislike of Monday’s for the first time.)
- September 19, 1978:
- September 20, 1978:
- September 21, 1978:
- September 22, 1978:
- September 23, 1978:
- September 24, 1978: (This strip is animated in Here Comes Garfield, a Garfield and Friends Quickie and "Long Lost Lyman Part 1".)
- September 25, 1978:
- September 26, 1978:
- September 27, 1978:
- September 28, 1978: (the 100th Garfield comic strip)
- September 29, 1978:
- September 30, 1978:
