The road, first designated in 1945, is located in Burnet and Williamson counties in the Texas Hill Country and passes through the city of Bertram and the smaller communities of Oatmeal and Mahomet.

RM 243 passes through a portion of a national wildlife refuge and crosses two forks of the San Gabriel River.

[1] US 183 was rerouted eastward south of Albany along a new route that includes the present section between Briggs and Austin at the Green's Corner terminus.

[4] The road proceeds northward passing through Oatmeal before crossing the South Fork of the San Gabriel River, then turns to the northeast toward Bertram.

[5][7] The road then passes through Mahomet before it terminates immediately after crossing into Williamson County at US 183 between Liberty Hill and Biggs.