The 1920–21 season was the 24th in the history of the Western Football League.
The Division One champions this season were Bristol City Reserves, for the second time in their history.
[1] Eight new clubs joined Division One this season, and the number of clubs increased from 10 to 16 after Horfield United and Newport County Reserves left the league.
Abertillery Town, Mid Rhondda, Pontypridd and Ton Pentre were also members of the Southern League (Welsh section) during this season.
Three new clubs joined Division Two this season, and the number of clubs increased from eight to ten after Yeovil and Petters United were promoted.