William Caldwell Plunkett (October 23, 1799 – January 19, 1884) was an American politician who served as the 20th Lieutenant Governor for the Commonwealth of Massachusetts from 1854 to 1855. In 1853 he was a delegate to the state Constitutional Convention. He lived in Adams for over 50 years and held many of the local offices.
He was born on October 23, 1799 in Lenox, Berkshire County, Massachusetts. He died on January 19, 1884 in Adams, Berkshire County, Massachusetts. His father was Patrick Plunkett; his mother was Mary Robinson. He first married Achsah Brown; after her death he married her niece Louisa Brown.
- Bevra Jane Pease Muirhead (1990), Judge Timothy Brown (1774–1852) Late of Elbridge, Onondage Co., NY. His Ancestry and Some of His Descendants, Eden, New York; Hamburg, New York: Artcraft Printing, Inc.
| Lieutenant Governor of Massachusetts
1854 – 1855