Andrew Ellicott (1754-1820) was an astronomer and surveyor. Prior to the Revolutionary War, Ellicott taught mathematics in Baltimore. A skilled surveyor, he conducted surveys of the Territory of Washington and the Mason-Dixon line. He also made the first topographical study of the Niagara River ad Falls. Ellicott was a member of the American Philosophical Society. He tutored Meriwether Lewis in astronomy before Lewis set out with Clark for their famous expedition. In 1813, Ellicott accepted a post as a professor of mathematics at West Point Academy. He died there in 1820.