Jasper County is a county in the U.S. state of Iowa. As of the 2020 census, the population was 37,813. The county seat is Newton. The county was organized in 1846 and is named after Sergeant William Jasper, a Revolutionary War hero.

Newton is the county seat of, and most populous city in, Jasper County, Iowa, United States. Located 30 miles (48 km) east of Des Moines, Newton is in Central Iowa. As of the 2020 Census, the city population was 15,760. It is the home of Iowa Speedway and Maytag Dairy Farms.