The 1920–21 season was the 12th in the history of the Isthmian League, an English football competition.
Ilford were champions, winning their second Isthmian League title.
League table
| Season | 1920–21 |
|---|---|
| Champions | Ilford |
| Matches played | 132 |
| Goals scored | 489 (3.7 per match) |
← 1919–20 1921–22 → | |
| Pos | Team | Pld | W | D | L | GF | GA | GR | Pts |
|---|---|---|---|---|---|---|---|---|---|
| 1 | Ilford | 22 | 16 | 4 | 2 | 70 | 24 | 2.917 | 36 |
| 2 | London Caledonians | 22 | 13 | 5 | 4 | 45 | 17 | 2.647 | 31 |
| 3 | Tufnell Park | 22 | 14 | 3 | 5 | 43 | 24 | 1.792 | 31 |
| 4 | Nunhead | 22 | 12 | 5 | 5 | 53 | 33 | 1.606 | 29 |
| 5 | Dulwich Hamlet | 22 | 11 | 6 | 5 | 60 | 30 | 2.000 | 28 |
| 6 | Oxford City | 22 | 12 | 3 | 7 | 56 | 38 | 1.474 | 27 |
| 7 | Leytonstone | 22 | 8 | 6 | 8 | 36 | 29 | 1.241 | 22 |
| 8 | Clapton | 22 | 7 | 7 | 8 | 33 | 52 | 0.635 | 21 |
| 9 | Civil Service | 22 | 3 | 7 | 12 | 28 | 45 | 0.622 | 13 |
| 10 | Woking | 22 | 3 | 5 | 14 | 16 | 43 | 0.372 | 11 |
| 11 | Casuals | 22 | 3 | 3 | 16 | 31 | 87 | 0.356 | 9 |
| 12 | West Norwood | 22 | 2 | 2 | 18 | 18 | 67 | 0.269 | 6 |