Lyon County Nevada Map shows the county’s location, the county seat, neighbouring counties, the state capital, and many more. Lyon County is located in west-central Nevada. Its total area is 2,024 sq mi (5,240 sq km), where 2,001 sq mi (5,180 sq km) land area and 23 sq mi (60 sq km) is water area. Yerington is the county seat and Fernley is the largest city.