Thousand Oaks is in the northwestern part of Greater Los Angeles, approximately 40 miles (64 km) from Downtown Los Angeles, and is less than 15 miles (24 km) from the Los Angeles neighborhood of Woodland Hills, halfway between Los Angeles and Santa Barbara, and 12 miles east of the Pacific Ocean. The city forms the central populated core of the Conejo Valley. The Los Angeles County–Ventura County line crosses at the city’s eastern border with Westlake Village. It is named after the many oak trees present in the area, and the city seal is adorned with an oak.

Designated open-space nature areas occupy 34 percent of the city (15,194 acres). 928 acres of the Santa Monica Mountains National Recreation Area (SMMNRA) is within the southern borders of the city. The physiography is dominated by prominent knolls, surrounding mountains, open vistas and native oak woodland. It is home to 50,000-60,000 oak trees, and the city is characterized by its many oak trees and rolling green hills.