Until 1937,
Colchester Town were Colchester's main club and were the original tenants of
Layer Road. Colchester Town joined the
Eastern Counties League in 1935, but their poor performances in the league convinced supporters that the club should turn professional, much like nearby
Ipswich Town. With club officials against the idea of turning professional, a new professional club was formed in March 1937,
Colchester United, which would also play at Layer Road. United joined the
Southern Football League as crowds for Town matches dwindled. In December 1937, Colchester United formed a reserve team, signing many of Town's players. As a result of this and Town struggling with
£300 debts, Colchester Town folded the same month. The club were Southern League champions in
1939 prior to the
Second World War. Following the war, in
1947–48, the U's produced one of the most notable
FA Cup runs by a non-league side, defeating fellow non-leaguers
Banbury Spencer in the first round, before beating Football League clubs
Wrexham,
Huddersfield Town and
Bradford Park Avenue. They finally fell to
Blackpool in the fifth round. This set them in good stead for potential election to the Football League. Colchester United were elected to the Football League in 1950 on the back of their second Southern League Cup win and ending the
1949–50 season second to
Merthyr Tydfil on
goal average alone. They spent eleven years in the
Third Division South and
Third Division following the league's reorganisation, with a best finish of third place in
1957, just one point behind rivals Ipswich Town and
Torquay United. The club suffered their first relegation in
1961 as they finished 23rd in the Third Division, but didn't have to wait long until their first Football League promotion, spending just one season in the
Fourth Division as they ended the season second to
Millwall by just one point. This trend continued over the next two decades as they were relegated to the Fourth Division in
1965 and promoted to the Third Division in
1966, then relegated in
1968 and promoted in
1974, relegated in
1976 and promoted in
1977 before a final relegation to the Fourth Division in
1981. During this time, the club embarked on one of the most notable runs in FA Cup history, as manager
Dick Graham took his ageing side to the
1970–71 quarter-finals, dispatching non-league
Ringmer,
Cambridge United,
Barnet and
Rochdale following a replay. With the draw having been made prior to the replay against Rochdale, the U's knew they would face a home tie with
First Division Leeds United, and duly trounced Dale 5–0. In the match with Leeds, the U's raced to an unprecedented 3–0 lead in front of a 16,000 Layer Road crowd, with two goals from
Ray Crawford and one from
Dave Simmons. Leeds did grab two goals back but Colchester held on for a famous 3–2 victory. The club faced
Everton in the quarter-finals but succumbed to a 5–0 defeat in front of 53,028 at
Goodison Park. Financial difficulties and a number of changes at board level in the mid-1980s caused a slide towards the lower end of the Fourth Division table and crowd numbers to dwindle. United were relegated from the Football League for the first time since their election. The club finished the season as runners-up to Barnet during their first season outside of the Football League, but, under the stewardship of
player-manager Roy McDonough, the U's won the league the following season on goal difference over bitter rivals
Wycombe Wanderers. In addition to earning a swift return to League football, the club also won the
FA Trophy in
1992. but did however reach the
Football League Trophy Final held at
Wembley. The U's drew 0–0 with
Carlisle United but were defeated 4–3 on
penalties. The following season however, Colchester were promoted via the
Third Division play-off final with a 1–0 Wembley win against Torquay United. , who guided the club to the
Championship for the first time in their history. Colchester consolidated their position in the third tier of English football for a number of seasons, before achieving their then-highest league finish of second place only to Essex rivals
Southend United in the
2005–06 season. Under
Phil Parkinson's stewardship, the U's were promoted to the second tier for the first time in their history. However, when Parkinson left to take the reins at
Hull City, his assistant
Geraint Williams was handed the daunting task of guiding Colchester into their first season in the Championship. He led the side to a 10th position finish, above
East Anglian rivals Ipswich Town,
Norwich City and Essex rivals Southend United, while gaining the
Pride of Anglia title in the process for the first time in their history. The momentum however did not continue into their second season in the Championship, as they finished bottom of the league and were relegated back to
League One. He was replaced by former Wycombe Wanderers manager
Paul Lambert as he guided the club to a mid-table finish. Colchester United started the
2009–10 season by thrashing recently relegated Norwich City 7–1 on the opening day of the season at
Carrow Road. Manager Lambert then defected to Norwich when their manager
Bryan Gunn was sacked following a poor start to the season. This ensured a fiery return fixture, held at the Community Stadium in January 2010. The season ended with Colchester finishing in 8th position. The club finished in 10th position for both the
2010–11 and
2011–12 seasons, before narrowly avoiding relegation to
League Two in the
2012–13 season, defeating Carlisle United 2–0 on the final day of the season to ensure their safety. The club then finished the
2013–14 season in 16th position. Colchester secured League One safety on the final day of the
2014–15 season when they beat promotion hopefuls
Preston North End 1–0 on 3 May 2015. However, Colchester could not stave off relegation to League Two in the
2015–16 season as they finished the campaign in 23rd position, confining them to the fourth tier of
English football for the first time in 18 years. In the
2019–20 EFL Cup, Colchester defeated Premier League side
Tottenham Hotspur on penalties. Colchester were eventually eliminated by
Manchester United in the quarter-finals, losing 3–0 at
Old Trafford. ==Colours and crest==