William H. Casselman (July 26, 1868 – July 1941) was an Ontario farmer and political figure. He represented Dundas as a United Farmers of Ontario member from 1919 to 1923.
He was born in Chesterville, Ontario, the son of James C. Casselman, and was educated in Chesterville and Morrisburg. In 1897, he married Flora Carlyle. He was defeated in the 1923 general election. Casselman later served several terms as reeve for Chesterville. He died in an accident on the farm while unloading hay.
His half-brother Orren D. Casselman served in the House of Commons.