State Route 266 is a west–east thoroughfare completely within Salt Lake County in northern Utah that connects both sides of the I-215 beltway. It is known as 4500 South and 4700 South along the route.

After its western terminus, SR-266 heads east to its western terminus, the only variation of the route being 4700 South veering two blocks to the north after SR-68 to become 4500 South.

The State Road Commission designated SR-266 in 1959 as a mostly-proposed roadway, connecting SR-68 and SR-71 with a planned interchange on I-15. The corresponding section of SR-174, just to the south, was removed from the state highway system, as it would not give access to I-15. The state legislature extended the route west and east to both sides of the I-215 loop in 1969.