Waldo is a village in Waldo Township, Marion County, Ohio, United States. The population was 326 at the 2020 census. Waldo is part of the River Valley Local School District.

Marion County is a county located in the U.S. state of Ohio. As of the 2020 census, the population was 65,359. Its county seat is Marion. The county was created in 1820 and later organized in 1824. It is named for General Francis "The Swamp Fox" Marion, a South Carolinian officer in the Revolutionary War.