The victory gives Troy the eighth and final slot in the Sun Belt Conference tournament that begins Thursday in New Orleans.
Troy held a 33-26 halftime advantage and stretched that 52-35 at the midway point of the second half. The Bobcats could not answer.
The Trojans won the rebound battle, pulling down 40 compared to 26 for Texas State.
Corey Stern and Kavin Gilder-Tilbury had 10 points apiece for the Bobcats (8-23, 4-14).