Belfast is a census-designated place (CDP) in Plainfield Township in Northampton County, Pennsylvania, United States.

Located in one of the first settled areas in the township, the village is believed to have been named for the city of Belfast in Northern Ireland.

Its settlers, who were predominantly German and Welsh, arrived in the area in the late 18th century.

[1] According to the U.S. Census Bureau, Belfast has a total area of 1.1 square miles (2.8 km2), all land.

The community is served by the Pen Argyl Area School District.