Nevada County is a county located in the U.S. state of California, in the Sierra Nevada. As of the 2020 census, its population was 102,241. The county seat is Nevada City. Nevada County comprises the Truckee-Grass Valley micropolitan statistical area, which is also included in the Sacramento-Roseville combined statistical area, part of the Mother L…Nevada County is a county located in the U.S. state of California, in the Sierra Nevada. As of the 2020 census, its population was 102,241. The county seat is Nevada City. Nevada County comprises the Truckee-Grass Valley micropolitan statistical area, which is also included in the Sacramento-Roseville combined statistical area, part of the Mother Lode Country.