Newton is the county seat of, and most populous city in, Jasper County, Iowa, United States. Located 30 miles east of Des Moines, Newton i…Newton is the county seat of, and most populous city in, Jasper County, Iowa, United States. Located 30 miles 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.