The South Green is located at the south end of Main Street which was laid out when Middletown was first established. In 1750-1755, the Protestant Episcopal Church was erected on an irregular triangular-shaped piece of property that was created by the intersection of Main and South Main Streets. Despite the fact that it was a marshy area and required drainage, it was a natural site because it was a major intersection and afforded a view of the Connecticut River (no longer visible).

When the church was removed, it opened up the intersection to be used as military training ground during the pre-Civil War era. In 1874, the horseshoe-shaped parcel then known as Union Park was formally landscaped. That same year, the Civil War memorial was dedicated and a bronze bust of Henry Clay Work on a granite base was placed on the green.

In the 1970s, the green was threatened by plans to re-route South Main Street (Route 17) which would have eliminated the green. However, the townspeople rallied and a compromise was reached; the green was enlarged at the expense of the historic road network.

The green's streetscape has changed dramatically over the years. Many of the buildings around the green built prior to 1800 were destroyed by fire. The only building from that era on its original site is a house constructed c. 1750. The area around the green became a fashionable residential neighborhood in the 19th century as demonstrated by the Mather-Douglas-Santangelo House (1811-1813) which commands the most impressive site along the green. Built by Mather, a wealthy Middletown businessman, it subsequently was used as a female seminary, and then was purchased by Douglas, another local businessman and a politician. South Green is still the focal point of religious activity as demonstrated by the three religious properties facing it, the Methodist and Episcopal (1869) church and the Adath Israel Synagogue.

South Green was the site of the first Episcopal Church and remains an important focal point of religious activity in Middletown with three religious properties presently ranged around it. It also serves as a southern terminus for Main Street and as a welcome open space in a somewhat dense urban environment.