William R. Leonard (born October 29, 1947) is a Republican U.S. politician who served as a member of the California State Board of Equalization from 2002 until his resignation in March 2010.

in history from the University of California, Irvine, Leonard worked in real estate and property management.

Leonard served on the Board of Directors of the San Bernardino Valley Municipal Water District before being elected to the California State Assembly in 1978 on the coattails of Proposition 13.

After term limits forced Leonard to leave the Assembly in 2002, he won election to represent the Second District on the five-member State Board of Equalization with 59% of the vote.

Leonard resigned from the State Board of Equalization in March 2010 in order to join Governor Arnold Schwarzenegger's administration.