William Hemsley (January 23, 1737 – June 5, 1812) was an American planter and political leader from Maryland.

Hemsley's entire life was closely connected with his family's plantation, Clover Fields Farm, in Queen Anne's County on Maryland's Eastern Shore.

He was a member of the Maryland Convention that ratified the United States Constitution on April 28, 1788.

He died there on June 5, 1812, and was buried in the family's cemetery on the farm, near Queenstown, Maryland.

His son, William Hemsley Jr., also served in the state senate in 1799–1800.