N.D. Cent. Code § 61-01-20: When special assessments shall become a lien

As between vendor and vendee, all special assessments upon real property levied pursuant to the provisions of this title shall become and be a lien upon the real property upon which the same are assessed, from and after the first day of January next after such assessments shall have been certified and returned to the county auditor, to the amount so certified and returned, and no more.