Pentwater is a village in Oceana County in the U.S. state of Michigan. The population was 857 at the 2010 census. The village is located within Pentwater Township. Pentwater is home to Mears State Park. The name Pentwater comes from Pent or Penned up waters. The entrance to the channel is notoriously shallow and for many years dictated the size of vessels that the village was able to accommodate.