Mahantango Creek rises in northern Schuylkill County between Line Mountain and Mahantango Mountain and flows west, eventually forming the boundary between Northumberland and Dauphin counties.
The source of Mahantango Creek is located in northern Schuylkill County, along the line formed by Line Mountain and Mahantango Mountain. The creek flows westwards and ultimately marks the boundary between Northumberland and Dauphin counties.