Miss. Code § 27-51-7
Any person required by law to pay a road and bridge privilege license tax on any motor vehicle shall also be liable for the ad valorem taxes due on such motor vehicle, unless otherwise specifically exempt herein. Such ad valorem taxes due shall be paid at the same time the road and bridge privilege license tax is paid, and the payment of the said ad valorem taxes due shall be a prerequisite to the issuance of the said road and bridge privilege license.
The ad valorem tax lien date for the purpose of this chapter shall also constitute the ad valorem tax due date which shall also be the same date that the subject motor vehicle is purchased from a bona fide dealer, if it is intended that such motor vehicle is to be operated upon the highways of this state.
In all cases, however, where the time for complying with the road and bridge privilege tax law has been extended by law as to time of payment, then the same extension of time shall apply to the date on which the ad valorem taxes on such motor vehicle must be paid. Ad valorem taxes on all motor vehicles, defined in this chapter, shall be calculated as of the first day of the month in which such taxes were due, regardless of any extension of time for payment of such taxes as provided hereinabove.
Miss. Code § 27-51-7