William Baylies (September 15, 1776 – September 27, 1865) was a U.S. Representative from Massachusetts, and brother of congressman Francis Baylies. His great-grandfather was Thomas Baylies, an ironmaster from Coalbrookdale, England, who emigrated to Boston in 1737. He was elected a member of the American Antiquarian Society in 1814. Baylies was then elected as a Federalist to the Thirteenth and Fourteenth Congresses (March 4, 1813 – March 3, 1817). He was elected as an Anti-Jacksonian to the Twenty-third Congress (March 4, 1833 – March 3, 1835).