Newmarket is a town in Rockingham County, New Hampshire, United States. The population was 8,936 at the 2010 census. Some residents are students and employees at the nearby University of New Hampshire in Durham.The primary settlement in town, where 5,297 people resided at the 2010 census, is defined as the Newmarket census-designated place, or CDP, and is located at the junction of New Hampshire routes 108 and 152, along the Lamprey River.