Sidley United were founded in 1906 and were founder members of Division Two of the
Sussex County League in 1952. Which they won in the
1958–59 season. By 1965 the club found themselves back in Division Two, however they won the Division straight away to win promotion back into Division One. The club alternated between Division One and Two for the next 21 seasons, which saw them twice finish runners up in Division Two in
1971 and
1978. During this period the club also made their debut in the
FA Cup in the 1973–74 season. It then took the club three seasons to get back up to Division Two when they won promotion into Division Two as runners-up in
1988–89. The
2000–01 season saw Sidley win Division One for the first time in their history, finishing five points ahead of
Burgess Hill Town, they also won the John O'Hara League Challenge Cup completing the league and cup double. The club gained promotion back to Division One at the end of the 2009–10 season, and completed a double by winning the Hastings Senior Cup as well. They remained playing in the league until 2013, achieving mid-table finishes. The club withdrew from the Sussex County League in 2013 due to the loss of their home ground following the financial collapse of the main social club and went without football that season but resumed playing in the ADA East Sussex Football League for the 2014/15 season in which they finished mid table. On 28 February 2015 their former clubhouse at The Gullivers was burnt down due to a fire. On 6 April 2016 they won the Sussex FA Junior Cup for the second time in their history by beating Wadhurst United 6 – 4 after extra time. The game had ended 3 – 3 with Sidley three times coming from behind. They clinched the Division One title later that month. After a couple of top half finishes, the Blues won the ESFL Premier Division in 2018/19. The club moved across into the Mid Sussex Football League for the next 3 seasons, winning the Championship Division in 2019/20 and Premier Division in 2021/22 as well as the Sussex FA Intermediate Cup that season before they returned to the East Sussex Football League. ==Stadium==