Can combine approx. 1,800 , 2100 or all units combined at 3,100 sqft contiguous. The City of Simi Valley, with an estimated population of 126,788 (as of July 2015) is the third largest of Ventura County's ten cities. Occupying an area of approximately 42 square miles, it is located in Southeast Ventura County, adjacent to the northwestern perimeter of the San Fernando Valley, approximately 37 miles northwest of downtown Los Angeles. The City was incorporated in 1969 under the general laws of the State of California and operates under a General-Law/council-manager form of government.