The Chicago Marathon is one of the flattest major marathons in the world—the closest thing to running a marathon on a track. It’s also one of the largest marathons in the world, but the city’s wide avenues afford each runner plenty of space to get in a good rhythm at PR pace. And no matter how fast you are, there are plenty of people to run with and push you along.
The weather in Chicago in early October is hit-or-miss. Some years, it’s cool and dry, and on those days, records are set, as when Joan Benoit Samuelson ran an American record of 2:21:21 in 1985. Other years it can be too wet, too windy, or way too hot to run fast.