The oldest building on the square is the Thomas Gibbons Range, at 102–116 West Congress Street, which dates to 1820.

The ward and square were named for Sir Matthew Decker, one of the Trustees for the Establishment of the Colony of Georgia in America, Commissioner of funds collection for the Trust, director and governor of the East India Company, and member of Parliament.

The square was renamed for Sir Henry Ellis, the second Royal Governor of the colony of Georgia.

It was also known as Marketplace Square, as from the 1730s through the 1950s it served as a center of commerce and was home to four successive market houses.

When the garage's lease expired in 2004, the city began plans to restore Ellis Square.