Middletown is a borough in Dauphin County, Pennsylvania, on the Susquehanna River, 10 miles (16 km) southeast of Harrisburg. As of the 2020 census, it had a population of 9,550. It is part of the Harrisburg–Carlisle Metropolitan Statistical Area.

Dauphin County is a county in the Commonwealth of Pennsylvania. As of the 2020 census, the population was 286,401. The county seat is Harrisburg, Pennsylvania's state capital and ninth-most populous city. The county was created on March 4, 1785, from part of Lancaster County and was named after Louis Joseph, Dauphin of France, the first son of King Louis XVI. The county is part of the South Central Pennsylvania region of the state.