Enter today! Of course you can enter at the door, but you'll save $27 and a long wait in line later this week.
The Chicago Open is at the Westin North Shore in Northbrook: choose between two-day, three-day, or four-day sections if you're under 2100, or the five-day Open section for strong players and masochists under 2100 (like me).
Details are here! The 2-day Under 1000 section is ideal for those new to tournament chess.