[1] Monticello was founded in 1837 as a commercial center for the future Piatt County, which was considered too far from Decatur to reasonably conduct trade there.

The original town plat covers all but four blocks of the historic district, with the remainder coming from one of the city's first additions.

The city received a major civic development in 1897, when the Town Hall and Opera House and the Allerton Library both opened in a new building.

[2] The Piatt County Courthouse, the focal point of the district, is a Classical Revival building designed by Urbana architect Joseph W. Royer.

The Romanesque Revival style makes a prominent appearance in the town hall and library building, which features a stone arched entrance and contrasting brickwork and stonework.