Penn Township is one of thirteen townships in St. Joseph County, Indiana, USA. As of the 2000 census, its population was 64,322.According to the United States Census Bureau, Penn Township covers an area of 63.58 square miles (164.7 km2); of this, 62.5 square miles (162 km2) (98.29 percent) is land and 1.08 square miles (2.8 km2) (1.71 percent) is water. St. Joseph County is a county located in the U.S. state of Indiana. Census 2010 put the population at 266,931. Formed in 1830, it was named for the St. Joseph River which flows through it toward Lake Michigan. The county seat is South Bend.