Alton is a town in Belknap County, New Hampshire, United States. The population was 5,894 at the 2020 census, up from 5,250 at the 2010 census. It is home to Alton Bay State Forest and Mount Major State Forest. The primary settlement in town, where 499 people resided at the 2020 census, is defined by the U.S. Census Bureau as the Alton census-designated place and is centered on the intersection of New Hampshire Route 11 and New Hampshire Route 140.