Peterborough is a town in Hillsborough County, New Hampshire, United States. The population was 6,418 at the 2020 census. The main village, with 3,090 people at the 2020 census, is defined as the Peterborough census-designated place (CDP) and is located along the Contoocook River at the junction of U.S. Route 202 and New Hampshire Route 101. Peterborough is 38 miles (61 km) west of Manchester and 72 miles (116 km) northwest of Boston.

Hillsborough County is the most populous county in the U.S. state of New Hampshire. As of the 2020 census, the population was 422,937, almost one-third the population of the entire state. Its county seats are Manchester and Nashua, the state's two biggest cities. Hillsborough is northern New England's most populous county as well as its most densely populated.