History:

New Haven County was constituted by an act of the Connecticut General Court on May 10, 1666, along with Hartford County Fairfield County and New London County. New Haven County consisted of the towns of Milford, New Haven, and Guilford. The town of Wallingford was established in 1670 in unincorporated area north of New Haven and formally added to New Haven County in 1671. In 1675, the town of Derby was established in the area north of Milford. In 1686, the town of Waterbury was established, but was assigned as part of Hartford County. Waterbury was later transferred to New Haven County in 1728. In 1722, most of northwestern Connecticut (except for the town of Litchfield) was placed under the jurisdiction of New Haven County. Eight years later, in 1730, the eastern half of northwestern Connecticut was transferred to the jurisdiction of Hartford County. By mid-1738, with the exception of the towns of New Milford, Sharon, and Salisbury, the entire territory of northwestern Connecticut was under Hartford County. In 1751, Litchfield County was constituted consisting of all the towns in northwestern Connecticut. Between 1780 and 1807, several more towns were established along the northern boundary of New Haven County, resulting in the alteration of the limits of the county. The final boundary alteration leading to the modern boundary resulted from the establishment of the town of Middlebury on October 8, 1807.