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Rock County is a county in the state of Wisconsin. Based on the 2010 census, the population was 160,331. Its county seat is Janesville.
Rock County comprises the Janesville-Beloit, WI Metropolitan Statistical Area and is included in the Madison-Janesville-Beloit, WI Combined Statistical Area.
Not named for its rocky soil (Gannett, Place Names, p. 222), nor for Rock Prairie therein (Wis. Hist. Colls., i, p. 113), but for its principal river. This stream was denominated by the early French explorers, "des Kickapoo," for a village of that tribe found upon it. In the eighteenth century it was called "Riviere de la Roche," which was variously translated into Stony, Rocky, and finally Rock River. This was no doubt a translation of the Indian word, given because of the chain of rocks at the mouth of the stream, causing the rapids beside which is now the city of Rock Island, Ill.
[Source: Kellogg, Louise Phelps. "Derivation of County Names" in Proceedings of the State Historical Society of Wisconsin for 1909, pages 219-231.]
County QuickFacts: CensusBureau Quick Facts
Rock county, created in 1836 as a territorial county, is named for the Rock River. Located in southeast
Wisconsin, the county seat is Janesville.
"ROCK, County, is bounded on the north by Dane and Jefferson, on the east by Walworth, on the south by the State of Illinois, and on the west by Green. The county seat is at Janesville, on Rock river. It was set off from Milwaukee, Dec. 7, 1836, and fully organized Feb. 19, 1839. The county is about equally divided between prairie and oak openings, with no large bodies of heavy timnber. It is situated on both sides of Rock river, the valley of which is as rich soil as can be found in any part of the country. The prairies are some of them quite large, but beautifully undulating, and productive in the highest degree, and are being settled and cultivated to the very centre. The different varieties of soil - upland, bottom land, prairie and openings, afford facilities for cultivating all the productions of the climate to the greatest advantage - wheat upon the rolling prairies and openings - the coarser grains upon the bottom lands - and tame and wild grasses upon the low prairies and marshes, flourish best, though each class of soil is adapted more or less to all these products. It is watered by Rock river and its branches. The principal villages are Janesville, Beloit, Fulton, and Milton. Its population in 1840 was 1,701; 1842, 2,867; 1846,12,405; 1847, 14,720; 1850, 30,717. Square miles, 720. It has 3,631 dwellings, 1,975 farms, and 126 manufactories"
Lies on both sides of Rock River, and is bounded on the south by Illinois. It is mostly prairie and openings,
there being no heavy timber. The prairies are more extensive than in other sections, Rock Prairie being the largest
in the State. The soil is exceedingly rich, especially in the valley of the Rock. The eastern part is not as well
watered as other portions. It is a thickly settled county. Janesville is the County Seat, and the fifth city in size
in the State, many routes of travel centering there. Beloit, in the southern part is a flourishing village, having
water power on the Rock River and Turtle Creek. It is the location of Beloit College, a well endowed and flourishing
institution, under the charge of the Wisconsin and Illinois Convention of Presbyterian and Congregational Churches.
The Milwaukee and Mississippi Rail Road passes through the northern part of Rock, having a branch from Milton to Janesville, which is ultimately to be continued west to the Mississippi, as the Wisconsin Southern. Rock River Valley Rail Road from the State line up the River. Beloit and Madison, now running about 18 miles from Beloit. Racine, having its terminus at Beloit, and the Kenosha and Janesville Road.
As reported by the Census Bureau, the county has a total area of 726 square miles (1,881 km2), of which, 720 square miles (1,866 km2) of it is land and 6 square miles (15 km2) of it (0.79%) is water.
Bordering counties are as follows: