A post office named Plainfield began operating here on April 5, 1826 with Smith serving as the first postmaster.

In 1828, the township was reorganized and renamed after attorney and statesman Henry Clay, and the post office was later renamed Clay on December 23, 1835; Smith continued serving as postmaster.

[30] The township contains a large portion of water that includes areas along the St. Clair River mouth in the northern Anchor Bay area of Lake St. Clair, which contains numerous channels and canals.

Directly across the river is the Walpole Island First Nation in Ontario, which is accessible via the Walpole–Algonac Ferry in downtown Algonac.

The St. Clair Flats State Wildlife Area and the majority of the St. John's Marsh State Wildlife Area are located within Clay Township.

22.9% of all households were made up of individuals, and 9.2% had someone living alone who was 65 years of age or older.