 Armstrong Township is bordered by Duboistown, South Williamsport, and the West Branch Susquehanna River to the north (with Williamsport, Loyalsock Township, and Montoursville north of the river), Brady and Clinton Townships to the south and east, Washington Township to the south, and Limestone, Bastress and Susquehanna Townships to the west.As the crow flies, Lycoming County is about 130 miles (209 km) northwest of Philadelphia and 165 miles (266 km) east-northeast of Pittsburgh.According to the United States Census Bureau, the township has a total area of .25.0 square miles (64.8 km2) of it is land and of it (2.11%) is water.