The county was formed on May 23, 1857 by act of the territorial legislature, but was not organized at that time. The area was designated Pipestone County, and the name Rock County was attached to the present Pipestone. In 1862 the Minnesota state legislature changed the designations, attaching the present names to the present counties. On March 5, 1870, the state legislature approved an act that finalized the county's organization and designated Luverne as the county seat. The county's name came from the Rock River, which in turn is named for a prominent rocky outcrop of reddish-gray quartzite, about 3 miles north of Luverne. The mound dramatically contrasts with the low surrounding prairie. Another source attributes the county name to its rocky soil.
Geography
Rock County lies at Minnesota's southwest corner. Its western border abuts South Dakota's eastern border; its southern border abuts Iowa's northern border. The Rock River flows southward through the east central part of the county, and Beaver Creek flows southward through the west central part of the county. The county consists of low rolling hills carved with drainages. The area is devoted to agriculture. The terrain slopes to the south, with its highest point near the midpoint of its north boundary, at 1,759' ASL. The county has an area of, of which is land and is water. The entire county falls in the hot summer humid continental climate zone.
Lakes
One of Minnesota's nicknames is "Land of 10,000 Lakes", and it is speckled with bodies of water large and small. But four of the state's counties do not contain a natural lake; Rock County is one of them. Rock County did host a manmade lake from 1938 until 2014: a WPA work project constructed a small dam on Blue Mounds Creek in 1938, creating a small lake in Blue Mounds State Park. This continued until June 2014, when the dam was damaged by rain and floodwaters, allowing the pond to drain. In June 2016 the Minnesota Division of Natural Resources announced its decision not to rebuild the dam.
As of the 2000 United States Census, there were 9,721 people, 3,843 households, and 2,705 families in the county. The population density was 20.2/sq. mi.. There were 4,137 housing units at an average density of 8.58/sqmi. The racial makeup of the county was 97.27% White, 0.53% Black or African American, 0.43% Native American, 0.62% Asian, 0.02% Pacific Islander, 0.53% from other races, and 0.59% from two or more races. 1.28% of the population were Hispanic or Latino of any race. 41.4% were of German, 23.8% Dutch and 16.5% Norwegian ancestry. There were 3,843 households out of which 31.30% had children under the age of 18 living with them, 62.10% were married couples living together, 5.50% had a female householder with no husband present, and 29.60% were non-families. 27.00% of all households were made up of individuals and 15.70% had someone living alone who was 65 years of age or older. The average household size was 2.47 and the average family size was 3.01. The county population contained 26.30% under the age of 18, 7.20% from 18 to 24, 24.10% from 25 to 44, 22.00% from 45 to 64, and 20.40% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 97.60 males. For every 100 females age 18 and over, there were 93.00 males. The median income for a household in the county was $38,102, and the median income for a family was $44,296. Males had a median income of $28,776 versus $22,166 for females. The per capita income for the county was $17,411. About 5.50% of families and 8.00% of the population were below the poverty line, including 8.10% of those under age 18 and 8.90% of those age 65 or over.
