Jordan Marsh is neither a person nor a landform - it was once the name of one of Boston's hometown department stores, and a pioneering firm in the market. For over one and one-quarter centuries, the company supplied much of New England with all manner of goods. However, in 1996, the brand was decommissioned.
In the same year, presumably at the time of renaming, a number of plaques (all identical) were placed on the outside of the Downtown Crossing location that was the hallmark of Jordan Marsh. These plaques read:
"This plaque commemorates the historic site of Jordan Marsh. In 1841, nineteen year old Eben Dyer Jordan began a remarkable and innovative journey that would lead to the founding, with partner Benjamin L. Marsh, of the renowned mercantile establishment whose flagship store was established at this location. Simultaneously, a young adventurer named Rowland Hussey Macy left his family home on Nantucket to begin a dry goods store in the heart of Boston. While this venture was short-lived, 'Captain' Macy gained valuable experience which eventually led to the creation of the famed retail landmark that bears his name. On March 25, 1996, the name Macy's came home to its roots as these two great institutions merged to begin a new era of retailing traditions throughout the New England community."
More information can be found at the link to Wikipedia below, or at Mass Moments.