 The Bank of America Chicago Marathon has grown significantly from its beginnings . In 1905 , 20 runners registered for the first Chicago Marathon , 15 actually started the race , and 7 finished . For the first " modern " marathon race in 1977 , just over 1 @,@ 000 people signed up for the race , with expected numbers of just 200 – 300 . In 1995 , 9 @,@ 000 people registered , and in 1999 , over 29 @,@ 000 people registered . The 2001 marathon run on October 7 reached its cap of 37 @,@ 500 , which was instituted after the 2000 race drew 33 @,@ 171 runners , just prior to the entry deadline on September 19 . In 2003 , 2004 , 2005 , and 2006 it reached its cap of 40 @,@ 000 . The October 10 , 2004 , October 9 , 2005 and October 22 , 2006 races reached their 40 @,@ 000 entrant caps on August 16 , July 14 , and May 26 respectively . On April 18 , 2007 , the 2007 race run on October 7 reached its cap of 45 @,@ 000 entrants . There was a late registration exemption whereby elite runners ( marathon times of less than 2 : 31 / 3 : 01 or half marathon times of 1 : 11 / 1 : 21 for ( men / women ) ) could register until September 1 even though the race had reached its registration cap in the spring . The 40 @,@ 000 registrants and 33 @,@ 000 finishers in 2003 made the Chicago Marathon the third or fourth largest marathon depending on which metric ( registrants or finishers ) is used . 
