This is one of the nicest racecourses in the country. It was built by Richard Duchesoise as his "personal" track, but was sold a few years ago to the Churchill Downs Corporation (who owns the Kentucky Derby.)

Trust me when I say that every detail has been scrutinized to make this one of the most beautiful public places there is. The grass and flowers are always totally vibrant. The personnel are always very friendly and the racing is always fun (though not always profitable.)

Live racing runs at the park for the whole summer, into late October.  They hold the Arlington Million race every year, which draws tons of people, not to mention some of the biggest horses in racing.  Most people find a day at the track to be very fun, even if they don't bet. 

Some things to consider:
First, the track is dark on Mondays and Tuesdays
There are usually concerts on the weekends, between the races.
Arlington has one of the biggest firework shows every Fourth of July.  It is done by the Grucci Brothers, and is outstanding.

You can get there on the Metra train from Chicago's Union Station. Check out their website at www.arlingtonpark.com.