Tex. Tax Code § 323.505

(a) The money received by a county under this chapter is for the use and benefit of the county and shall be used for the replacement of property tax revenue lost as a result of the adoption of the taxes authorized by this chapter. Except as provided by Subsection (b), the revenue in excess of the revenue used to replace those property taxes shall be used for the reduction of indebtedness of the county. After all indebtedness is paid, the excess may be used for any purpose for which county general revenue may be used. A county may not pledge anticipated revenue from this source to secure the payment of bonds or other indebtedness for a period longer than one year.

(b) Revenue collected from the tax imposed under this chapter in each of the first three years in which the tax is imposed in the county in excess of the amount determined as provided by Section 26.041(d) for each year shall be deposited in an account to be called the excess sales tax revenue fund. During those three years, revenue deposited in the excess sales tax revenue fund may be used only if and to the extent that taxes or other revenues of the county are collected in amounts less than anticipated. After that period, the revenue in the fund may be used for any purpose for which county general revenue may be used. The fund ceases to exist when all revenue deposited in the fund has been spent.