Cinco de Miler
The Chicago Cinco de Miler run is an annual 5 mile race that happens around May 5th each year. The race, which is billed as Chicago's only stand alone 5 miler, celebrates Mexico's colorful culture, and is half fun run/half "see how fast you can go" road race.
The race field is usually quite large, recently attracting 4,000+ participants, many of whom end up running it in some sort of Mexican themed costume. In addition to the usual gear (shirt etc.) you can expect a pretty solid post race area complete with beer garden, and appropriately themed snacks (think chips, salsa, and churros). If you're looking for a fun themed race with a good mix between road racing and a fun run this is an event that we'd recommend considering.
The Cinco de Miler course follows a looped course through the park and along the waterfront. The course is flat, and, although it features a few turns, still runs quite fast.