Chautauqua County is the westernmost county in the U.S. state of New York. As of the 2020 census, the population was 127,657. Its county seat is Mayville, and its largest city is Jamestown. Its name is believed to be the lone surviving remnant of the Erie language, a tongue lost in the 17th century Beaver Wars; its meaning is unknown and a subject of speculation. The county was created in 1808 and organized in 1811. The county is part of the Western New York region of the state.