[1] State maintenance and the SH 172 designation begin along the shore of Keller Bay in the Calhoun County community of Olivia.

[2] The route travels northward along the peninsula and into Jackson County, where it intersects SH 35 in the hamlet of Weedhaven.

SH 172 continues to the north and has a brief concurrency FM 616 in La Ward before turning slightly to the northwest.

The SH 172 designation ends at Loop 522, the former route of US 59 through the city; 3rd Street continues northward as FM 710.

[4] On January 9, 1934, the route was extended to Olivia, replacing part of SH 111, which was rerouted further north.