SLCF serves as area of over 268 square miles in the southern portion of Lake County. Napa County bounds the District on the south, Sonoma County on the west, the Kelseyville Fire Protection District on the north, and the Lake County Fire Protection District on the north/east.

In 1949, SLCF annexed the areas of the geothermal geyser industry. In October of 1989, the District annexed 6,500 acres in the Loch Lomond area. At this time, mutual aid agreements have also been developed with CDF/Napa County for fire and EMS services on Highway 29 between the Napa County line and Robert Louis Stevenson Memorial State Park as well as the area of the Lake/Napa County line in Butts Canyon.