HILLSBORO, a city of Illinois, U.S.A., 5om. N.E. of Saint Louis ; the county seat of Montgomery county. It is served by the Chicago and Eastern Illinois, the Big Four and the Illinois Trac tion (electric) railways. The population in 192o was it was 4,435. Farming, dairying and coal-mining are the principal occupations of this region. There is a large electric-power plant in the city, as well as zinc smelters, a fruit-jar factory, and brick, tile and concrete works. Hillsboro was settled about 1823. It was incorporated as a town in 1855, and as a city in 1882.