"Mount Clare" — also known as "Mount Clare Mansion", known today as the Mount Clare Museum House — is the oldest Colonial-era structure in the City of Baltimore, Maryland, U.S.A. The Georgian style of architecture plantation house exhibits a somewhat altered five-part plan. It was built on a Carroll family plantation beginning in 1763 by barrister Charles Carroll the Barrister, (1723-1783), a descendant of the last Gaelic Lords of Éile in Ireland and a distant relative of Charles Carroll of Carrollton, (1737-1832), longest living signer of the Declaration of Independence and the richest man in America in his later years, also the layer of the "first stone" of the new Baltimore and Ohio Railroad, just a short distance away in 1828.