Woodlawn's monumental stone barn stands beside the Federal-style home, built about 1794 by Richard Thomas. Woodlawn ran a girl's boarding school that was attended by a daughter of Francis Scott Key, author of the "Star Spangled Banner," who rode horseback three hours from his Georgetown home to visit. The plantation had a grist mill powered by water flowing from the Sandy Spring. In 1832 Dr. William P. Palmer, owner after the Thomases, commissioned master stone mason Isaac Holland to build the extravagant barn--the only large stone barn in Maryland.

Quaker doctor William P. Palmer purchased Woodlawn from the Thomases in 1822. As a youth he made sailing voyages to England and China as a captain's clerk. He became an incorporator and director of the Mutual Insurance Company. At the country physician's death in 1867 the Annals observed: "He always made visits on horseback, and never knew any distinction between those who paid him and those he called 'God Almighty's patients.'"