Johns Hopkins' father Samuel freed his slaves in 1807 and put his sons to work on the family tobacco plantation. In 1812, an uncle took Hopkins in with him as a wholesale grocer and commission merchant in Baltimore, and two years later put him in charge while he was away for an extended period. Even with the British fleet threatening Baltimore, Hopkins carried on. In 1819, he and his uncle disputed--during a depression--whether to accept whiskey rather than cash as payment for merchandise.

Johns and three brothers established their own firm. He expanded into neighboring states and a variety of endeavors, including banking, warehousing, and railroading. He was the third largest investor in the Baltimore and Ohio Railroad, behind the city and the state. At his death, he left $7 million to build a hospital, nursing school, medical school, and a university.