Middlefield is a town in Middlesex County, Connecticut, United States. The population was 4,203 at the 2000 census. The town includes the village of Rockfall in the northeast section.

Middlefield, in Middlesex County, is so named because it is halfway between Middletown and Durham, and Middletown and Meriden. For such a small community, Middlefield has an abundance of wonderful history that goes back to the late 17th century and many first settlers of Connecticut. The Old North Burying Ground was established for those living west of Middletown and the first burial was in 1738.

Middlefield became a town in 1866 by an act of the Connecticut Legislature. The town was previously part of the City of Middletown.

First Selectmen Charles R. "Charlie" Augur (in office 1995–2005) and Jon A. Brayshaw (in office 2005-2015) having both served five terms as First Selectman have been the longest-serving First Selectmen of the town. Dr. Harold Ellsworth Smith, son of Dr. Ernest Ellsworth Smith and his wife Lilian Irene [Church] Smith, was Middlefield's physician for 45 years.

Middlesex County was created on May 2, 1785 from Hartford and New Haven counties. The county was named for Middlesex, England. Middlesex County is in south-central Connecticut. It is bordered to the south by Long Island Sound and to the southwest by the Hammonasset River, and the Connecticut River bisects the county from north to south. Other waterways are the Menunketesuck River, the Moodus Reservoir, and Bashan Lake. The topography is mostly upland terrain, with river valleys and coastal lowlands. Parklands include Cockaponset State Forest, Meshomasic State Forest Preserve, and Hurd and Devil's Hopyard state parks.

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