William B. Lewis (c. 1816 – October 15, 1884) was an American businessman and politician.
He began to work as a brick hod carrier, then learned the builder's trade, and became a contractor.
In the 1850s, he was City Comptroller of Brooklyn.
He was New York State Treasurer from 1862 to 1863, elected on the Union ticket nominated by the Republicans and War Democrats.
After the American Civil War he left politics, and became the Secretary and Cashier of the Brooklyn City Railroad and held these posts until his sudden death, collapsing on Fulton Street, Brooklyn. Sometime prior to his death he had removed to Plainfield, New Jersey, but commuted to Brooklyn every day.