Tex. Const. art. XVI, § 61

(a) All district officers in the State of Texas and all county officers in counties having a population of twenty thousand (20,000) or more, according to the then last preceding Federal Census, shall be compensated on a salary basis.

(b) In all counties in this State, the Commissioners Courts shall be authorized to determine whether precinct officers shall be compensated on a fee basis or on a salary basis, with the exception that it shall be mandatory upon the Commissioners Courts, to compensate all justices of the peace, constables, deputy constables and precinct law enforcement officers on a salary basis.

(c) In counties having a population of less than twenty thousand (20,000), according to the then last preceding Federal Census, the Commissioners Courts have the authority to determine whether county officers shall be compensated on a fee basis or on a salary basis, with the exception that it shall be mandatory upon the Commissioners Courts to compensate all sheriffs, deputy sheriffs, county law enforcement officers including sheriffs who also perform the duties of assessor and collector of taxes, and their deputies, on a salary basis.

(d) All fees earned by district, county and precinct officers shall be paid into the county treasury where earned for the account of the proper fund, provided that fees incurred by the State, county and any municipality, or in case where a pauper's oath is filed, shall be paid into the county treasury when collected and provided that where any officer is compensated wholly on a fee basis such fees may be retained by such officer or paid into the treasury of the county as the Commissioners Court may direct.

(e) All Notaries Public, county surveyors and public weighers shall continue to be compensated on a fee basis.