The county was established on May 23, 1857, by an act of the territorial legislature, although it was not organized at that time.

However, in 1862, the Minnesota state legislature changed the designations, assigning the present names to the respective counties.

This outcrop is composed of reddish-gray quartzite and is located approximately 3 miles (4.8 km) north of Luverne.

The county is characterized by the flow of the Rock River, which runs southward through its east central part, and Beaver Creek, which flows southward through its west central region.

[5] The terrain gradually slopes southward, with the highest point situated near the midpoint of the county's northern boundary, reaching an elevation of 1,759 ft (536 m) above sea level.

[7] The entire county falls within the hot summer humid continental climate zone (Dfa).

One of Minnesota's nicknames is "Land of 10,000 Lakes", and it is speckled with bodies of water large and small.

[9] Rock County did host a manmade lake from 1938 until 2014: a WPA work project constructed a small dam (the "Lower 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.

[10] In June 2016 the Minnesota Department of Natural Resources announced its decision not to rebuild the dam.