State Route 138 is a highway,[2] completely within Tooele County in northern Utah that connects Grantsville to Erda and Stansbury Park.

It runs northeasterly until terminating at Mills Junction north of Stansbury Park, at milepost 62.9 of Highway 36.

With the exception of the segment between SR-112 and Sheep Lane, the route is included in the National Highway System.

[3] The current route of SR-138 was formed in 1965, when SR-2 was moved to the north to reflect the future alignment of then under-construction I-80.

[3] In the May 2018 meeting of the Utah Transportation Commission, a motion passed to truncate the east end SR-138 to the future Tooele Midvalley Highway (SR-179).