Plymouth is a town in Grafton County, New Hampshire, United States, in the White Mountains Region. Plymouth is located at the convergence of the Pemigewasset and Baker rivers. The population was 6,990 at the 2010 census. The town is home to Plymouth State University, Speare Memorial Hospital, and Plymouth Regional High School.The town's central settlement, where 4,456 people resided at the 2010 census, is defined as the Plymouth census-designated place, and is located along U.S. Route 3, south of the confluence of the Baker and Pemigewasset rivers.