Utah State Route 100 (SR-100) is a state highway in the U.S. state of Utah. Located entirely in Millard County, it connects the city of Fillmore with Flowell and the ghost town of McCornick over a distance of 16.9 miles (27.2 km).

The route begins as 400 North at SR-99 (Main Street) in Fillmore. From here, it travels west out of town, crosses over I-15. After 4.6 miles (7.4 km), the route turns north and continues through rural Millard County for about 12.3 miles (19.8 km) until it ends at US-50.

SR-100 was originally established in 1935 as connecting Fillmore at SR-1 (Main Street) and Flowell. The construction of I-15 through the area resulted in the old alignment of the route along 100 North to be severed in two by the interstate, so in 1965, the route was moved north three blocks to its current alignment along 400 North because of the proposed underpass on that street.

In 1969, the 12.6 miles (20.3 km) from near Flowell northward to US-50 was transferred to the route, resulting in its current length and alignment.

The entire route is in Millard County.