Teams were placed into two separate leagues, Eastern Division and Western Division. With the winners of each league playing in a play-off to decide the overall winner.
Clubs
The league featured 17 clubs, 11 which competed in the 1939–40 season, along with six new clubs:
Source: Sussex County league - Historic League Tables Rules for classification: 1) points; 2) goal difference; 3) number of goals scored. The points system until the 1982–83 season: 2 points for a win, 1 point for a draw and 0 points for losing.
Source: Sussex County league - Historic League Tables Rules for classification: 1) points; 2) goal difference; 3) number of goals scored. The points system until the 1982–83 season: 2 points for a win, 1 point for a draw and 0 points for losing.