William Caldwell Plunkett (October 23, 1799 – January 19, 1884) was an American politician who served as the 20th lieutenant governor of Massachusetts from 1854 to 1855.
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.
Married 22 Apr 1839 in Elbridge, Onondaga County, New York by Rev J.