The county stretches roughly 65 miles (105 km) from Sacramento's suburbs at Roseville to the Nevada border and the shore of Lake Tahoe.

[6] Miners washed away the gravel, leaving the heavier gold, in a process known as "placer mining".

Gold mining was a major industry through the 1880s, but gradually the new residents turned to farming the fertile foothill soil, harvesting timber and working for the Southern Pacific Railroad.

The building was renovated during the late 1980s and continues to serve the public with courtrooms, a sheriff's office and the Placer County Museum.

Loomis and Newcastle began as mining towns, but soon became centers of a booming fruit-growing industry, supporting many local packing houses.

Lincoln also is the home of one of the county's oldest businesses, the Gladding, McBean terra cotta clay manufacturing plant, established in 1875.

[8] The county is typically divided into three regions; "South Placer" in the Central Valley and the Sierra Nevada foothills south of Auburn, "Gold Country" which consists of the Sierra Foothills around Auburn, Colfax, and Foresthill, and the Sierra Nevada which consists of all areas east of Foresthill and northeast of Colfax (including the Lake Tahoe region).

Roughly 3/4ths of the population lives in South Placer, Roseville being the primary job and retail center of the county.

It provides patrol, detective, and other police services for the unincorporated areas of the county plus by contract to the city of Colfax and the town of Loomis.

[29] Between 1916 and 1976, however, the county voted Republican only in three landslide elections of 1920, 1952 and 1972 – in all of which its GOP margins were much smaller than for the state or nation.

In the California State Senate, Placer County is split between the 1st, 4th, and 6th districts,[31] represented by Megan Dahle, Marie Alvarado-Gil, and Roger Niello, respectively.

In the California State Assembly, the county is split between the 1st, 3rd, and 5th districts,[32] represented by Heather Hadwick, James Gallagher, and Joe Patterson respectively.

The following table includes the number of incidents reported and the rate per 1,000 persons for each type of offense.