Mount Gay-Shamrock is a census-designated place (CDP) in Logan County, West Virginia, United States.

[2] The CDP includes the unincorporated communities of Mount Gay, Shamrock, Black Bottom, Whites Addition, Lintz Addition, Thompson Town, Hedgeview, Ridgeview, Logan Heights, Cora, and Whitman Junction.

[6] Mount Gay-Shamrock is located in west-central Logan County,[1] with the village of Mount Gay in the eastern part of the CDP at the confluence of Island Creek and the Copperas Mine Fork,[7] and the village of Shamrock just to the west in the valley of the Copperas Mine Fork.

The CDP is bordered to the east by the city of Logan, the county seat, and to the west by U.S. Route 119, a four-lane freeway which separates Mount Gay-Shamrock from Verdunville.

West Virginia Route 44 leads south from Mount Gay up the valley of Island Creek.

Old US Highway 119 runs up the valley of the Copperas Mine Fork, joining current US-119 at Holden.