Allendale Charter Township, Michigan. Allendale Charter Township is a charter township of Ottawa County in the U.S. state of Michigan. As of the 2010 census, the township population was 20,708. It is a part of the Grand Rapids-Muskegon-Holland, Michigan combined statistical area, and is an exurb of Grand Rapids, due to its major commuter routes into the city (M-45 and I-96).