Denton County, Texas was created out of Fannin County on April 11, 1846, shortly after the state abandoned its dream of being a Republic and joined the United States. Pioneers, attracted to the North Texas area by the Texas Emigration and Land Company - known as the Peters Colony - had begun building homes in the wilderness along the Trinity River and its tributaries during the days of the Republic of Texas.

The first Anglo settlements in Denton County began in the mid-1840s near Hebron in the southeast corner of the county, Pilot Point in the northeast and Little Elm on the eastern border with Collin County. Pioneer settlements soon spread north and south through the east Cross Timbers and into the Grand Prairie.

Colonists named their new county Denton in honor of pioneer preacher, lawyer and Indian fighter John B. Denton who was killed by Indians in 1841. They chose a county seat along Pecan Creek and named it Pinckneyville in honor of Texas Governor J. Pinckney Henderson.

Water shortages forced the county seat to be moved twice, first in February 1848 to a site named Alton in what is now Corinth. In 1849, the county seat moved again to a nearby location on Hickory Creek also called Alton. By 1856, Alton boasted a blacksmith shop, three stores, several homes and a cemetery, a saloon, a hotel and bar, two doctors, several lawyers and was headquarters for the Denton County Land District.

By 1857, however, Denton County was again looking for a new county seat more central to the settlements in Pilot Point to the north and Lewisville to the south. Alton residents voted to move again. This time they named the new county seat Denton. The original township lots were auctioned on January 10, 1857.

For a decade, Denton County was on the frontier of North Texas. John Chisum, who became one of the most famous cattlemen in the country after he moved to New Mexico, operated his first ranch in Denton County. When the Civil War took many men away, the frontier settlements were left unprotected. Indian attacks increased. On moonlit nights, Comanche and Kiowa raiders from the Indian Territory rode across the Red River to steal horses and cattle in Texas. The last Indian raid in Denton County was reported in August 1874.

In 1875, the county courts building on the north side of the square burned, destroying most of the county records. A two-story brick courthouse was then built in the center of the downtown Denton square. The new structure was condemned after being struck by lightning and was demolished in 1894. Construction of the Courthouse-on-the-Square began in 1895, the cornerstone was laid in 1896 and the courthouse was dedicated in 1897. The courthouse still stands in the center of downtown Denton. County offices are now located in several county buildings, but the Denton County Commissioners Court, the County Commissioners offices, the Office of Economic Development and the Courthouse-on-the-Square Museum are still housed in the old Courthouse-on-the-Square.

Ranching and subsistence farming gave way to cotton farming in the blackland prairie and wheat farming on the grassland prairies as railroads entered the county in the 1870s.

Denton embarked on a course that made it a center for higher education when North Texas Normal College, now the University of North Texas, was established in 1890 and the College of Industrial Arts, now Texas Woman's University, was created in 1901.

Denton County today is also a center for horse ranching and light industry and a balanced farming region producing wheat, cotton, beef, and dairy cattle. Lewisville, Carrollton, Flower Mound, The Colony and Denton are major urban centers.