In Maryland, if you are behind at least $250 on property taxes, those taxes become a lien on your property. A lien is a debt that is attached to your property, like a mortgage. In Baltimore City you must be behind at least $750 to face tax sale.
So, Maryland state tax liens can eventually expire, but the statute of limitations is very long: 20 years.
(2) If the property is subject to a special valuation under § 7-211 of this article, a lien: (i) arises on the date on which the interest in the property vests in possession; and (ii) continues for 20 years.