The Big Annemessex River is a 15.4-mile-long (24.8 km) tributary of the Chesapeake Bay on the Delmarva Peninsula. It rises in Kingston, Somerset County, Maryland, and flows roughly southwest about 6 miles (10 km) in a meandering pattern, then widens into an estuary and continues about 9 miles (14 km) to the bay, near Janes Island State Park.