Del. Code tit. 9, § 8427

The receiver of taxes and county treasurer or director of finance shall deposit in any depository bank or credit union in the State at the county seat, to the credit of the county, all public money received, within 3 days of the receipt thereof. The same shall remain therein, unless determined by the county government to be idle or surplus and thereupon by order or authorization invested in accordance with § 4122 of this title, or until drawn in payment of legal demands, or in the transfer thereof to a successor.