Tex. Government Code § 74.054

(a) Except as provided by Subsections (b) and (c), the following judges may be assigned as provided by this chapter by the presiding judge of the administrative region in which the assigned judge resides:

(1) an active district, constitutional county, or statutory county court judge in this state;

(2) a senior judge who has consented to be subject to assignment and who is on the list maintained by the presiding judge under this chapter;

(3) a former district or appellate judge, retired or former statutory probate court judge, or retired or former statutory county court judge who certifies to the presiding judge a willingness to serve and who is on the list maintained by the presiding judge as required by this chapter;

(4) a retiree or a former judge whose last judicial office before retirement was justice or judge of the supreme court, the court of criminal appeals, or a court of appeals and who has been assigned by the chief justice to the administrative judicial region in which the retiree or former judge resides for reassignment by the presiding judge of that region to a district or statutory county court in the region; and

(5) an active judge or justice of the supreme court, the court of criminal appeals, or a court of appeals who has had trial court experience.

(b) An active statutory county court judge may not be assigned to hear a matter pending in a district court outside the county of the judge's residence.

(c) A constitutional county court judge may only be assigned to sit for another constitutional county court judge and must be a licensed attorney in this state.

(d) A retired judge of a statutory probate court may also qualify for assignment under Section 25.0022.