Ellis Square is one of the 22 squares of Savannah, Georgia, United States. It is located in the northernmost row of the city's five rows of squares, on Barnard Street and West St. Julian Street, and was one of the first four squares laid out. Today, it marks the western end of City Market. The square is east of Franklin Square, west of Johnson Square and north of Telfair Square. The oldest building on the square is the Thomas Gibbons Range, at 102–116 West Congress Street, which dates to 1820.

Decker Square, as it was originally known, was laid out in 1733 as part of Decker Ward, the third ward created in Savannah. 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. Prior to Union General Sherman's arrival in December 1864, it was also the site of a slave market with some indications of slaves being held under the northwest corner of the square. A large brick building, now known as the John Montmollin Building, was built in 1855 to house the slave market, facing south on Barnard Street.

In 1954, the city signed a 50-year lease with the Savannah Merchants Cooperative Parking Association, allowing the association to raze the existing structure and construct a parking garage to serve the City Market retail project. Anger over the demolition of the market house helped spur the historic preservation movement (most notably the Historic Savannah Foundation) in Savannah. The outer structure of this city market building influenced the design of the Kroger grocery store on Gwinnett Street and the Publix grocery store in the Twelve Oaks shopping center on Abercorn Street.