The Chicago Marathon has set a cap on the number of participants that are allowed to take part in the 2009 race. The cap for participants has been set at 45,000. According to emails sent out on Monday, April 21st the race is getting very close to reaching full capacity. If you are one of those people who are toss around the idea of running then I suggest that you sign up in a hurry.
The last few years I have known of many runners that have tried to wait until June or July to sign up for Chicago and they discovered that the race was already full. Chicago is one race that easy reaches capactiy five or six months ahead of race day due to its relatively flat course and very fast times.
You can sign up for the 2009 Chicago Marathon by visiting their registration page or by visiting their website.