William Henry Purnell (1826–1902) was the Comptroller of Maryland from 1856–1861.
Prior to his election as comptroller Purnell served as lawyer. In 1846 Purnell had received a degree from Delware College (now the University of Delaware).
Purnell was elected to office as a member of the Know-Nothing Party. He was reelected in 1860, but later quit office to take an appointment as post master of Baltimore and then served as a Union Army officer in the United States Civil War. Purnell had raised a military unit for the Union cause, known as Purnell's Legion, in Worcester County, Maryland. Purnell resigned from the military, holding the rank of colonel, in February 1862 and resumed the position of post master of Baltimore. This resignation was endorsed by Major General John Adams Dix.
In 1870 Purnell became the president of Delaware College, a position he retained until 1885.
Purnell married Margaret Neill Martin. They were the parents of ten children.
- Roger D. Hunt. Colonel in Blue: Union Army Colonels in the Civil War, The Mid-Atlantic States. (Mechanicsburg, Pennsylvania: Stackpole Books, 2007) p. 277