For most of its history, Eastern Counties 3 was divided into two regional divisions – north and south – with teams from Cambridgeshire, Norfolk, Suffolk and Essex taking part.

A breakaway of Essex teams at the end of the 2002–03 to form a new league would lead to Eastern Counties 3 being abolished by the end of 2003–04 only to return due to a league restructure to cater for more 2nd and 3rd teams.

[1] The creation of National 5 South meant that Eastern Counties 3 dropped from a tier 10 league to a tier 11 league for the years that National 5 South was active.

The cancellation of National 5 South at the end of the 1995–96 season meant that Eastern Counties 3 reverted to being a tier 10 league.

After an absence of nine years, Eastern Counties 3 was re-introduced as a tier 11 league ahead of the 2014–15 season, this time split into three regional divisions - north, south and west.