Marathon is a city in Buena Vista County, Iowa, United States. The population was 302 at the 2000 census. The food writer Richard Olney grew up in Marathon.
Marathon is located at 42°51′36″N 94°58′54″W / 42.86°N 94.98167°W / 42.86; -94.98167 (42.860021, -94.981731).
According to the United States Census Bureau, the city has a total area of 0.7 square miles (1.9 km²), all of it land.