New Marlborough is made up of the villages of Clayton, Hartsville, Mill River, Southfield, & New Marlborough Center. There are also several other districts and areas that are only sparsely settled, these include the Canaan Valley, the Huxley District, Norfolk District, and East Indies. Its greatest population was in 1875 during a period of intense agricultural growth. Mill River became the political center of the Town because some twenty small mills developed along the Konkapot River. They consisted of saw mills, grist mills, paper mills, a buttery, a creamery, a marble saw mill, a brass foundry, and a gunpowder mill. The result was that the Town Hall was located there in 1871.
The Town was named after Marlborough, Massachusetts in Middlesex County where its first Proprietors divided up the lots of Township No. 2 along the Indian path from Westfield to Sheffield in 1738. The first settler was Benjamin Wheeler who arrived in the summer of 1739 and built his Regulation house on Lot 25, First Division, located on Anthony Brook. He wintered over to 1740, his only companions were the members of the Mahaican Tribe (Stockbridge Indians) under Sachem Anthony. The following spring the Wards, Blackmers, Keyes, Alexanders, Thomases, Bullards, & Rawsons arrived. History has it that the first white children born in New Marlborough were twins of Phillip Brooks and wife who were wintering in the Town Fort on Leffingwell Hill in the winter of 1758. They had arrived too late in the season to finish their house in the Norfolk District. Collar, Cleveland and Hyde families followed.
The first church was established at New Marlborough Center in 1744 and the first building erected on Lot No. 22 in 1743. By 1793 discussion about a new church was underway and the people of Southfield agreed to establish and build a second church in their village. The North and South Parishes were largely established before the American Revolution. This resulted in North and South Companies of Minutemen before the revolution.