Local Government Code §171.010

(a) For purposes of this chapter, a county judge or county commissioner engaged in the private practice of law has a substantial interest in a business entity if the official has entered a court appearance or signed court pleadings in a matter relating to that business entity. (b) A county judge or county commissioner that has a substantial interest in a business entity as described by Subsection (a) must comply with this chapter. (c) A judge of a constitutional county court may not enter a court appearance or sign court pleadings as an attorney in any matter before: (1) the court over which the judge presides; or (2) any court in this state over which the judge's court exercises appellate jurisdiction. (d) Upon compliance with this chapter, a county judge or commissioner may practice law in the courts located in the county where the county judge or commissioner serves.