At the new plantation, which they called Poplar Hall, John was schooled by his parents and by a series of tutors. In 1750 and at age 18, John began reading law in Philadelphia and later in England at Middle Temple, Inns of Court and Westminster. Returning home in 1757, he began law practice in Philadelphia. Active in the Pennsylvania Assembly, he attended the Stamp Act Congress where his suggested resolutions were adopted with few changes. His Letters of a Farmer in Pennsylvania written in 1767, brought him fame. As a result, Dickinson was called on for advice and inspiration in the years before the First Continental Congress.

After John's death in 1808, the plantation remained in the family until the 20th Century, when it passed through a series of owners. In 1952, the National Society of the Colonial Dames of America in the State of Delaware purchased the mansion with 12 acres for $25,000. They presented the site to the State in Constitution Day ceremonies that year. The Mansion opened as a museum in May 1956, after 3 1/2 years of restoration.