Early voting in Illinois started yesterday and Cook County Clerk David Orr stated that "turnout is already impressive", with 13,500 Cook County suburban voters casting ballots. That's compared to 7,700 suburban Cook County ballots cast on the first day of 2008 early voting. However, the window for early voting is shorter this year than 2008.
The clerk's Web site provides locations for where Cook County residents can cast their ballot prior to November 6. You don't need an excuse to vote before election day, but, unlike on election day itself, you do need a valid photo ID.