Essex County is a county in the U.S. state of New York. As of the 2020 census, the population was 37,381. Its county seat is the hamlet of Elizabethtown. Its name is from the English county of Essex. Essex is one of two counties that are entirely within the Adirondack Park, the other being Hamilton County. The county is part of the North Country regio…Essex County is a county in the U.S. state of New York. As of the 2020 census, the population was 37,381. Its county seat is the hamlet of Elizabethtown. Its name is from the English county of Essex. Essex is one of two counties that are entirely within the Adirondack Park, the other being Hamilton County. The county is part of the North Country region of the state.