White settlers were drawn to the area by rumors of gold and by land opened through the Homestead Act
of 1862. However, it was the discovery of rhyolite
stone, not gold, that ultimately led to its settlement.
Castle Rock was founded in 1874 when the eastern Douglas County border was redrawn to its present location. This city was chosen as the county seat because of its central location.
One of the first homesteaders in the area near today’s Castle Rock was Jeremiah Gould. He owned about 160 acres (0.65 km2) to the south of “The (Castle) Rock.” At that time, the settlement consisted of just a few buildings for prospectors, workers, and cowboys. In 1874, Jeremiah Gould donated 120 acres (0.49 km2) to the new town that was also now home to the Douglas County government. For the beginning the six streets named Elbert, Jerry, Wilcox, Perry, Castle and Front were laid out to build the actual town of Castle Rock. The Courthouse Square was defined and about 77 lots, each 50 by 112 feet (34 m), were auctioned off for a total profit of US$
During the late 1800s and early 1900s, Castle Rock had a very active Rhyolite
quarrying industry. Many Swedish immigrants arrived in the area to work in the quarries.
Castle Rock currently encompasses about 35 square miles (91 km2), with a population of more than 42,000
in town and 70,000 in the surrounding area