1. Chelsea (jointly with Arsenal) were the first clubs to play with numbered shirts – on 25 August 1928 in their match against Welsh side Swansea City.
2. Chelsea’s highest appearance-maker is Ron Harris, who played in 795 first-class games for the club between 1961 and 1980.
3. With 86 caps, Frank Lampard is Chelsea’s most capped international player.
4. Bobby Tambling is Chelsea’s all-time top goal scorer, with 202 goals in 370 games (1959–70).
5. Chelsea hold the record for the highest ever points total for a league season (95) and the fewest goals
conceded during a league season (15) – under the management of Jose Mourhino in 2004/05.
6. Chelsea became the first British side to field an entirely foreign starting line-up in a Premier League match – against Southampton in December 1999.
7. The club’s 21–0 victory over Jeunesse Hautcharage in the UEFA Cup Winners’ Cup in 1971 remains a record in European competition.
8. On 19 May 2007, they became the first team to win the FA Cup at the new Wembley Stadium.
9. Chelsea hold the record for the longest streak of unbeaten matches at home in the English top-flight, which lasted 86 matches from 20 March 2004 to 26 October 2008.
10. Chelsea holds the record for the highest home attendance match – against Arsenal with an attendance of 82,905 on the 2 October 1935.
11. Chelsea’s mascot is a lion taken from their club logos and named Stamford The Lion. In July 2005 the costume was stolen from Stamford Bridge.
Source: http://www.hitc.com/en-gb/2011/07/07/11-facts-about-chelsea-that-chelsea-fans-already-know/