It is part of the Dallas-Fort Worth-Arlington metropolitan statistical area, and a small portion of the city of Dallas is in the county.

[3] In the mid 1840s, a Kiowa chief named Spotted Tail moved his band to the area between Frisco and Prosper.

Unlike the rest of the American South, slavery never took a strong hold in Collin County due to the lack of navigable rivers and railroads to transport cash crops to market where it could be sold.

Muster rolls recorded more than 1,500 men enlisted to fight for the Confederacy[13] with Throckmorton himself leading his own company of mounted rifleman.

While Bob Lee was ambushed and killed by soldiers from the 6th Cavalry Regiment in 1869, retaliatory violence did not stop until the assassination of Lewis Peacock in his home in 1871.

[8] The city of Allen, Anna, and Melissa owe their names and existence to those associated with the Houston and Texas Central Railroad.

[16][17][18] Collin County, originally reliant on corn and wheat,[8] began to shift its agricultural production to produce more cotton with the arrival of the railroads.

In 2019, the American Community Survey estimated its non-Hispanic white population now represented 55%, reflecting a national demographic trend of diversification.

[38] American Community Survey 2023 Data The United States Census Bureau estimated that in 2023, Collin County’s population was 1,195,359.

By the 2020s, Collin County had become considered competitive in national elections due to demographic and voting trends, though it remains Republican-leaning.

[43] Despite its Republican lean, Collin County has trended leftward, as Joe Biden managed to win 46.9% of the vote share (compared to Donald Trump's 51.3%) in the 2020 presidential election, the best result for a Democrat since 1964.

[55][56] The North Central Texas Council of Governments (NCTCOG) in a 2022 meeting discussed the possibility of expansion of the Red Line corridor from Plano through Allen to McKinney.

[59][60] In January 2025, city officials approved a $72 million project to build a commercial airline terminal on the east side of the airport.

[62] Carrollton, Frisco, Prosper, and Celina are served by a BNSF Railway line connecting Irving to Denison.

[63][64] McKinney is the southern terminus of a branch line of the Dallas, Garland and Northeastern Railroad that originates in Sherman.

[66] The sanctuary was established by Bessie Heard in 1967 in order to preserve natural spaces from expansion in the Dallas–Fort Worth metroplex.

Local media outlets are KDFW-TV, KXAS-TV, WFAA-TV, KTVT-TV, KERA-TV, KTXA-TV, KDFI-TV, KDAF-TV, and KFWD-TV.

Other nearby stations that provide coverage for Collin County come from the Texoma market, including KTEN-TV and KXII-TV.

Newspapers in the Collin County area include the Allen American, Celina Record, Farmersville Times, Frisco Enterprise, McKinney Courier-Gazette, and the Plano Star-Courier.