William Henry Harrison Llewellyn (September 9, 1851 – June 11, 1927) was a member of the New Mexico House of Representatives.

During the Spanish–American War, Llewellyn and his son, Morgan, served with the Rough Riders in the United States Army under the command of future U.S. President Theodore Roosevelt.

Llewellyn died at the William Beaumont Army Medical Center on June 11, 1927.

During this same time, Roosevelt appointed Llewellyn's son Morgan to be Surveyor General of the New Mexico Territory.

After the territory achieved statehood, Llewellyn was a member of the New Mexico House of Representatives in 1912.