Newmarket is a town in Rockingham County, New Hampshire, United States. The population was 9,430 at the 2020 census. Some residents are students and employees at the nearby University of New Hampshire in Durham. The densely settled center of town, where 5,797 people resided at the 2020 census, is defined as the Newmarket census-designated place and is located at the junction of New Hampshire routes 108 and 152, along the Lamprey River.