A borough of Dauphin county, Pennsylvania, U.S.A., on the east bank of the Susquehanna river, 9 m. below Harrisburg. Pop. (1890), 5080; (1900), 5608, of whom 340 were foreign-born and 289 negroes. It is served by the Pennsylvania and the Philadelphia & Reading railways, and by an electric line to Harrisburg. The borough has a considerable trade with the surrounding agricultural country, and owing to the proximity of the Yorkhaven power-plant (across the river) and the excellent railway service, is a manufacturing centre. The municipality owns its electric lighting plant. Middletown was founded in 1 755 by Friends (from Philadelphia and other places in Pennsylvania) and Scotch-Irish, and was so named because of its position midway between Lancaster and Carlisle. It was first incorporated as a borough in 1828.