The 1921 South Australian Football League season was the 42nd season of the top-level Australian rules football competition in South Australia.
The competition expanded from seven to eight teams with being admitted to the seniors after one year in the B Grade (Reserves).
The season opened on Saturday 7 May with the opening fixture between and , and concluded on Saturday 8 October with the Grand Final, in which Minor Premiers went on to record its 9th premiership, defeating by 8 points.
, also made the top (final) four teams and participated in the finals series. , , , all missed the top four. Glenelg finished winless (as they also did in next three seasons 1922âÂÂ1924) to "win" the wooden spoon in its first season.