Sandoval Township (W½ T2N R1E) is centered at 38°36'N 89°7'W (38.362, -89.068). It is transversed north-south by U.S. Route 51 and east-west by U.S. Route 50. The city of Sandoval is located in the center of the township and Junction City is located in the southern part. According to the 2010 census, the township has a total area of 17.6 square miles (46 km2), of which 17.54 square miles (45.4 km2) (or 99.66%) is land and 0.06 square miles (0.16 km2) (or 0.34%) is water.
Prior to 1896 Sandoval Township was the western part of Odin Township.