Local Government Code §115.045

(a) A county with a population of 350,000 or more shall conduct an annual independent audit of all books, records, and accounts of each district, county, and precinct officer, agent, or employee, including the regular county auditor, and of all governmental units of the county hospitals, farms, and other institutions. The audit shall cover all matters relating to the fiscal affairs of the county. (b) The commissioners court of the county shall employ a disinterested, competent, experienced public accountant or certified public accountant to perform the audit. The court shall contract for the audit at the regular January meeting of the court. The consideration specified in the contract shall be paid from the general fund of the county. (c) The audit required under this section is in addition to any special audit prepared under Subchapter C or to any regular or special audit report prepared by the regular county auditor.