New Philadelphia was founded by Frank McWorter, a free African American, in 1836. New Philadelphia was the first town planned in advance and legally registered by an African American in the United States, and it likely served as a stopping place for the "Underground Railroad" of enslaved African Americans who were fleeing northward from the oppression of southern plantations. The site of New Philadelphia was located in Hadley Township, not far from the Mississippi River valley to the west and the Illinois River valley to the east.

At the time it was founded, proposed construction of an Illinois-Michigan canal had helped spur the establishment of a number of towns, including New Philadelphia and the town of Barry a few miles away. New Philadelphia developed as a town at a crossroads in this agricultural area through the 1860s, with an active roadway carrying agricultural products and other goods to the Mississippi River, 20 miles to the west. The community also grew within a region torn by racial strife, with clashing factions of pro-slavery and abolitionist interests in Hannibal, Quincy, Jacksonville, and Alton. The town size grew to approximately 160 people, 29 households, and several craftspeople and merchants by 1865.