Texas Local Government Code - LOC GOV'T § 116.058. Amount of Security Required

(a) Personal or surety bonds that secure county deposits must be in an amount equal to the estimated highest daily balance of the county, as determined by the commissioners court. However, the commissioners court may not estimate the highest daily balance at an amount that is less than 75 percent of the highest daily balance of the county for the preceding year, less the amount of bond funds received and expended.

(b) Securities pledged to secure county funds on deposit in a depository must be in an amount equal to the amount of those funds. However, real property securities may not be required in an amount greater than 25 percent of the assessed value of the property in the county, as shown by the certified tax roll for the preceding year.