- Total 3,616 sq mi (9,370 km2)
- Land 3,299 sq mi (8,540 km2)
- Water 317 sq mi (820 km2)
Highest elevation 5,109 ft (1,557 m)
Population (April 1, 2010)
- Total 269,637
- Estimate (2016) 282,887
- Density 86/sq mi (33/km2)
The prehistory of San Luis Obispo County is strongly influenced by the Chumash people who had significant settlement here at least as early as the Millingstone Horizon thousands of years before the present age. Important settlements existed, for example, in many coastal areas such as Morro Bay and Los Osos.
Mission San Luis Obispo de Tolosa was founded on September 1, 1772 in the area that is now the city of San Luis Obispo. The namesake of the mission, city and county is Saint Louis of Toulouse, the young bishop of Toulouse (Obispo and Tolosa in Spanish) in 1297.
San Luis Obispo County was one of the original counties of California, created in 1850 at the time of statehood.
The Salinas River Valley, a region that figures strongly in several Steinbeck novels, stretches north from San Luis Obispo County. The remote California Valley near Soda Lake is the region most untouched by modernity. Travels through this area and the hills east of highway 101 during wildflower season are very beautiful and can be incorporated with wine tasting at local vineyards.