JANESVILLE, one of the most flourishing and important towns in the State, the county-seat of Rock County, is beautifully located on both sides of Rock River, forty-five miles southeast of Madison. It contains eight churches, three banks, several academies, seminaries, the State Institution for the Blind, manufactories and mills of various kinds, and five newspapers. The Milwaukee and Mississippi Railroad is here intersected by the Fond du Lac and Rock River Road. There are other railroads in course of construction, which, when completed, will largely increase its extensive trade. In 1846, the population was estimated at 400; in 1854, at 6,000; and, at present time, about 10,000.