Developed most intensively in the late 19th and early 20th centuries, this area was the center of commerce for Waterville and the surrounding rural communities.

The city's most rapid period of growth was between about 1890 and 1920, when many of the brick commercial buildings lining Main Street were built.

Castonguay Square, a grassy park on the north side of Common Street and south of City Hall, was laid out in 1796, when the area was still part of Winslow.

The Opera House and City Hall, a single building on the north side of Castonguay Square at the corner of Front Street, is a fine example of Colonial Revival architecture, and continues to serve the community as an entertainment venue and municipal center.

The district's oldest building is the 1836 Ticonic Row (8-22 Main), which exhibits Greek Revival features overlaid by alterations made in the 1920s.