The center of Fairfield Township is located at (38.7405671, -98.8698075) at an elevation of 1,893 feet (577 m) [REF].
According to the United States Census Bureau, Fairfield Township occupies an area of 40.20 square miles (104.1 km²) of which 40.19 square miles (104.1 km²) is land and 0.01 square miles (0 km²) is water [REF].