Plainfield Charter Township is a charter township of Kent County in the U.S. state of Michigan. According to the 2010 census, the population was 30,952. The township forms part of the metro Grand Rapids area. It derives its name from the extinct lumbertown of Plainfield founded in 1838 by Andrew Stout at the intersection of the Rogue and Grand Rivers. The town name was eventually changed to Austerlitz before its eventual dissolution.