Which changes were the big ones?
Change score: the share of the course (averaged both ways) that is more than 60 m from the previous marathon's course. 0 means the same course; 100 means a completely new one.
Bar height = how much the course changed from the previous marathon. Click or drag to pick a year.
Winning times
Open-division winners. Ringed points are world records. The strip below marks the years the course changed.
Finishers
From 2,128 in 1977 to more than 54,000 in 2025. No race in 2020; 1987 was a half marathon.
Race-day temperature vs. winning time
Men's open winners. Average 7am–noon temperature at Grant Park (ERA5 reanalysis).
How far north and south
Northernmost and southernmost points of each course, in Chicago street-grid addresses.
The most-run streets
Number of races that used at least 0.1 mi of each street.
Course family tree
How much of each course is shared with each other course. Solid blocks along the diagonal are eras when the course held steady.
Neighborhoods on the course
Chicago community areas each course ran through (at least 0.1 mi).