Fort Ross, California. Fort Ross is a former Russian establishment on the west coast of North America in what is now Sonoma County, California, in the United States. It was the hub of the southernmost Russian settlements in North America between 1812 to 1842. It has been the subject of archaeological investigation, and is a California Historical Landmark, a National Historic Landmark, and on the National Register of Historic Places. It is part of California's Fort Ross State Historic Park.