Chicago Marathon

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First run on 25 September 1977 as the Mayor Daley Marathon, named for Richard J. Daley, who had backed the idea and died in office the previous December. More than 4,000 runners started, a very large field for the period, and the race was won by Dan Cloeter in 2:17:52 and Dorothy Doolittle in 2:50:47. The course is a loop that starts and finishes in Grant Park and covers a flat lakeside city on a grid, with almost no gradient and a start-finish separation of essentially zero, so it satisfies both record-eligibility criteria with enormous margin. It is where Kelvin Kiptum ran 2:00:35 on 8 October 2023 and where Ruth Chepngetich ran 2:09:56 on 13 October 2024. Its weakness is the calendar: an early-October date in a continental climate makes it the Major most exposed to a hot year.