Marathon is a city in Buena Vista County, Iowa, United States. The population was 230 at the time of the 2020 census. The food writer Richard Olney grew up in Marathon. From 1996 to 2017, every year in June, a marathon, half-marathon and 5k were held in the city. It was USA Track and Field certified and sanctioned, allowing participants to be eligible to qualify for the Boston Marathon.