[2] RM 187 begins at its southern terminus with US Highway 57 (US 57), near Batesville,[3][4] as a paved, two-lane, asphalt road.

[9][10] RM 187 winds through nearly seven miles (11 km) of brushland, passing several large ranches and farms alongside the Sabinal River.

The highway heads through the unincorporated community of Vanderpool[7] and runs concurrently with RM 337 for a length of 1.1 miles (1.8 km).

Separating and running northward,[11] RM 187 continues along the southwestern edge of the Lost Maples State Natural Area.

On November 23, 1948, it was extended to a point 4.3 miles (6.9 km) south of Sabinal, while the previous extension was cancelled and redesignated FM 1023.