Juncus cooperi is a species of rush known by the common name Cooper's rush. It is native to the deserts of the southwestern United States and northern Mexico, where it grows in alkaline and saline soils such as those around salt marshes and desert springs. This is a perennial herb forming large clumps of erect stems up to about 80 centimeters tall from a thick rhizome and large root network. The bases of the stems are surrounded by sparse, small leaves, which are stiff and have sharp tips.