The first known explorer to have set foot in what is now known as Sargent's Purchase was Darby Field, who claimed to have made the first ascent of Mount Washington in 1642. Sargent's Purchase was granted to Jacob Sargent and others on May 31, 1832. In May 1866, Sylvester Marsh of Campton, New Hampshire, began construction of the Mount Washington Cog Railway, primarily in Thompson and Meserve's Purchase, but the uppermost half mile being within Sargent's Purchase. The Cog Railway was completed in 1869.