William Henry Cain (October 31, 1792 - August 20, 1878) was an American plantation owner and politician; he served as the lieutenant governor of South Carolina from 1846 to 1848.
A graduate of South Carolina College, he purchased the plantations Somerset and Somerton in 1827 with Isaac Marion Dwight.
In 1841 he was elected to the South Carolina State Senate to replace a member who had resigned, and he served there until 1845.
As executor, he petitioned the legislature for compensation for a slave named Frank who was executed for trying to poison his master.
Cain is buried in St. Stephen's Episcopal Church Cemetery, Berkeley County, South Carolina.