Newmarket, town (1991 pop. 15,861), Suffolk, E England. It has been a horse-racing center since early in the 17th cent. There are four principal races: the One Thousand Guineas, the Two Thousand Guineas, the Cambridgeshire, and the Cesarewitch. One of the courses on Newmarket Heath is crossed by the ancient "Devil's Dyke." Newmarket is also the home of the Jockey Club. Wicken Fen, a nearby nature reserve, is one of the only remaining parts of the Fens.