 Fallowfield Township has nine land borders, including Carroll Township to the north, North Charleroi, Charleroi and Twlight to the east, California and West Pike Run Township to the south, Bentleyville to the southwest, Somerset Township from the west to northwest and Nottingham Township to the north-northwest.A short segment of Fallowfield Township in the northeast corner runs adjacent with Monessen across the Monongahela River in Westmoreland County, 
At the 2000 census there were 4,461 people, 1,765 households, and 1,313 families living in the township.The population density was 209.6 people per square mile (80.9/km²).