William Van Ness Bay (November 23, 1818 - February 10, 1894) was a U.S. Representative from Missouri.
Born in Hudson, New York, Bay attended the public schools there. Following his primary education, Bay studied law and was admitted to the bar. He moved to Union, Missouri, in 1836 and commenced the practice of law. He served as member of the State house of representatives 1844-1848.
Bay was elected as a Democrat to the Thirty-first Congress (March 4, 1849-March 3, 1851). After his term ended, he resumed the practice of law.
He was appointed judge of the State Supreme Court in 1862. Bay was elected to the position in 1863 and served until removed by Governor Fletcher in 1865. He moved to St. Louis, Missouri, and again resumed the practice of law. He retired in 1886 and moved to Eureka, Missouri, where he died February 10, 1894. He was interred in Oak Hill Cemetery, Kirkwood, St. Louis County, Missouri.