Nevada County is a county located in the Sierra Nevada of the U.S. state of California, in the Mother Lode country. As of 2000 its population was 92,033. The county seat is Nevada City.

According to the U.S. Census Bureau, the county has a total area of 974 square miles, of which, 958 square miles of it is land and the remaining 17 square miles (1.73%) is water.

The western part of the county is defined by the course of several rivers and the irregular boundaries of adjoining counties. When the county was created, the founders wanted to include access to the transcontinental railroad, so a rectangular section was added that includes the railroad town of Truckee. What is remarkable about this is that the final shape of the county closely resembles the Deringer pocket pistol, a favorite at the time of the more urbane residents of this gold rush county.

Nevada County was created in 1851 from parts of Yuba County.

The county was named after the mining town of Nevada City, a name derived from the term "Sierra Nevada." The word nevada in Spanish means "snowy" or "snowcovered."