Salem Township (T2N R2E) is centered at 38°36'N 88°59'W (38.619, -88.980). It is traversed north-south by Interstate Route 57 and State Route 37 and east-west by U.S. Route 50. The city of Salem is located in the northeastern part of the township as is most of the Salem Reservoir (El. 166 m). According to the 2010 census, the township has a total area of 35.72 square miles (92.5 km2), of which 35.38 square miles (91.6 km2) (or 99.05%) is land and 0.34 square miles (0.88 km2) (or 0.95%) is water.