Texas Election Code - ELEC § 271.008. Ballot Boxes

(a) One set of ballot boxes may be used at a common polling place in a joint election for the deposit of all the ballots for each of the participating political subdivisions.

(b) If the voted ballots for more than one political subdivision participating in a joint election are deposited in a single ballot box after they are counted, the custodian of the key to the ballot box for voted ballots for elections ordered by an authority of any one of the participating political subdivisions may be appointed as the custodian of the key to that box.