The highway was originally designated on August 4, 1932 from Hondo southeast to Devine.

[7] On September 3, 1935, a road from Devine to Jourdanton was being investigated for preparation for restoration of this section of SH 173.

[8] On September 26, 1939, the designated route was extended south from Jourdanton through Freer, absorbing most of SH 241, with an expected terminus at Hebbronville.

SH 173 runs northwest toward Devine where it intersects I-35 in the south part of town.

Leaving Devine, 173 turns running in a sharper northwest direction.