Middletown was founded in 1755 along the left bank of the Susquehanna River and was incorporated as a borough in 1828 after a sudden boom in development and population occurred as a result of the construction of the Union Canal, connecting Lancaster to Middletown. Earlier in 1824 the Commonwealth of Pennsylvania's legislature authorized and funded the canal construction as part of the broad sweeping commercial initiative called the Main Line of Public Works; a forward looking project designing to connect Philadelphia to Pittsburgh by canals and river navigations which projects would continue to allow Philadelphia to challenge New York City (and its Erie Canal) for emerging mid-western markets beyond the Allegheny Mountains. Middletown was selected as the western terminus of the Union Canal, and it was named from its location halfway between Lancaster and Carlisle, where an ascent exists to a low pass allowing easier (wagon era) travel among the barrier mountains of the Ridge-and-valley Appalachians giving access into north-central Maryland and the valley of the Potomac River. It is the oldest incorporated community in Dauphin County and is located within a rich agricultural area forming the western edge of Pennsylvania Dutch Country.