The Office of Finance for New Castle County shall on or before December 15 of each year, make at least 1 demand in writing upon every person or corporation liable for the payment of any taxes collectible by the County and due and then remaining unpaid for the payment thereof, stating the amount due and that, if the same are not paid during the month of December, legal proceedings will be instituted for the collection thereof. The failure to give notice shall not constitute a bar to any of the proceedings hereinafter authorized and directed. The notice shall be mailed in a sealed postpaid envelope directed to the last known address of the person or corporation, and the day of the mailing shall be deemed the day of the giving of notice.