Collin County (C-18/19), is located in northeastern Texas thirty miles south of the Red River. McKinney, the county seat, is thirty-four miles northeast of Dallas. The county's center lies at approximately 33°11' north latitude and 96°34' west longitude. With the exception of a small portion of its western edge, Collin County's area of 851 square miles lies entirely within the Blackland Prairie region of Texas. The surface of the county is generally level to gently rolling, with an elevation ranging from 450 to 700 feet above sea level. Deep clayey soils over marl and chalk surface the central and western part of the county. Dark loamy alluvial soils, subject to flooding during the rainy season, lie in the eastern section. The western and central portions of the county are drained by the East fork of the Trinity River. The Elm fork of the Trinity drains the eastern section. Bois d' arc, oak, elm, ash, pecan, and post oak trees grow along the streams of the county but not in sufficient quantity for commercial use. Limestone and sand for making cement are the only mineral resources. Temperatures range from an average high of 96° F in July to an average low of 34° in January. Rainfall averages just under thirty-five inches a year, and the growing season extends for 237 days.
Branches of the Caddo Indians inhabited the area before the arrival of the first White settlers. Occasional outbreaks of violence occurred between the two groups, but there was no extended period of conflict since the Caddos withdrew from the county by the mid-1850s. The absence of organized Indian resistance, combined with the county's fertile soil and an offer of land grants by the Peters colony attracted settlers to the area in the early 1840s. Even with the offer of free land, the estimated population of the county was only 150 when it was demarked from Fannin County on April 3, 1846, and named for Collin McKinney, one of the first settlers of the county and a signer of the Texas Declaration of Independence. The original county seat was Buckner. Because this town Buckner was not within three miles of the center of the county, however, McKinney became the county seat in 1848. Like the county, McKinney was named for Collin McKinney.
The settlement of Collin County can be divided into two phases. The first occurred during the early period of the county's history, from 1840 to 1860. The second phase took place during and after the arrival of railroads. The settlements established before the construction of rail lines seldom survived if the railroads bypassed them. The majority of the first settlers of Collin County were farmers who lived near streams, where water and wood were easily obtained. They established small, family-operated farms that produced mostly wheat and corn. The slave and cotton economy that characterized most of the South, with its large plantations, failed to take hold in the county. In part this was a result of the lack of navigable rivers and railroads to transport cash crops to retail centers. The nearest market was Jefferson, more than 150 miles to the east. In addition, the farmers who settled the county were from the upper South and had little experience in slaveholding or raising cotton. In 1860 only 1,047 of the 9,264 residents were black, and the cotton harvest was of no significance.
These factors, plus the influence of James W. Throckmorton, a native of McKinney and Texas state senator, resulted in Collin County's vote against secession, 948 to 405, in 1861. Once Texas joined the Confederacy, however, more than 1,500 residents of the county enlisted in the defense of the South, led by Throckmorton, who rose to the rank of brigadier general. During the war isolated incidents of violence occurred between Union sympathizers and Confederates, including the participation of an undetermined number of county residents in the events that led to the Great Hanging at Gainesville in 1862. Outbreaks of violence continued after the war. Farmersville, twelve miles east of McKinney, was the site of one of the killings that took place during the Lee-Peacock feud. By 1869 gunplay between the two groups had ended. Except for the military appointments of a few public officials in 1867–68, the county remained under the control of the Democratic party during Reconstruction.
For the first thirty years of the county's history farmers had little incentive to take advantage of the fertile soil of the Blackland Prairie, considered the richest agricultural region of Texas. Between the 1840s and 1870s the lack of transportation facilities, limited markets, and absence of mechanized farm equipment restricted the agricultural production of the county. The arrival of the railroad removed these obstacles and initiated a fifty-year period of economic growth. In 1872 the Houston and Texas Central Railway, the first to reach the county, connected McKinney and Plano to tracks that reached as far south as Houston. The Missouri, Kansas and Texas followed four years later and was joined in a decade by the Gulf, Colorado and Santa Fe. By the mid-1890s six railroads crisscrossed the county, connecting farmers to retail markets throughout Texas. With an outlet for their products farmers began to cultivate the unplowed fertile land in the eastern and central sections of the county. Between 1870 and 1920 the number of farms and crop production increased dramatically. In 1870, 903 farms valued at just over three million dollars produced 674,565 bushels of corn, 4,371 bales of cotton, and 42,827 bushels of wheat. In 1920 the number of farms had increased to 6,001, with a value estimated at well over $84 million. Production of corn had increased to 2,574,689 bushels, cotton to 49,311 bales, and wheat to 956,412 bushels.
By the 1920s, twenty-three Collin County communities had voted road bonds totaling just under $4 million. New roads, combined with State Highway 289, provided county residents with easy access to Dallas, Fort Worth, and Waco. By the end of the decade thirteen communities had electricity, natural gas, and a telephone exchange. Three had a population of over 1,000. In 1920 the county seat had 6,677 residents, and the population of the county was 49,609.
During the next forty years, however, the population declined. The Great Depression, mechanization of farms, and employment opportunities outside the county contributed to the drop in population. Although Collin County did not suffer the extreme hardships that befell other areas of Texas, the number of county farms declined from 6,069 in 1930 to 4,771 by 1940. The value of all crops harvested dropped from just over $10 million to just over $6.5 million during the same period. As late as 1940 Collin County's unemployment rate stood at 19 percent.
By the mid-1950s the economy had recovered. The average value of farmland per acre increased from $58.91 in 1940 to $145.52 in 1954. In part this improvement was a result of the efforts of the Texas Research Foundation and the Collin County Soil Conservation District. The Texas Research Foundation, established at Renner in 1944, used the latest scientific discoveries to improve farming practices. In 1946 the Collin County Soil Conservation District was formed and planned the construction of 144 flood-retarding structures, including Lake Lavon, to prevent the flooding of thousands of acres of rich bottomland in southeastern Collin County. Farmers also benefited from the electric cooperatives established by the Rural Electrification Administration in the late 1930s. The Hunt-Collin Co-operative (1937), the Fannin County Electric Co-operative (1939), and the Grayson-Collin Electric Co-operative (1937) combined to bring electricity to the isolated communities of the county. New roads also assisted county farmers. In 1946 the county had 138 miles of paved roads. By the early 1970s the paved miles had increased to 2,333. The work of the Texas Research Foundation and improved soil-conservation practices increased the production of wheat, the county's primary cash crop, from 352,229 bushels in 1949 to 1,224,664 bushels in 1959.
The mechanization of farming, however, reduced the number of farms from 3,166 in 1950 to 2,001 in 1960. A corresponding decline in the county's population occurred. Historically the percentage of tenant farmers in Collin County was high; it reached a peak of 74 percent in 1925. By 1960 that figure had dropped to 38 percent. Because of the lack of business opportunities outside farming in the county, the majority of those forced to leave farming also left the county. The population decreased from 47,190 in 1940 to 41,247 in 1960.
Although agriculture, especially developing dairy farming, continued to be an important factor in the county's economy, by 1980 the introduction of light industry, combined with the growth of the Dallas metropolitan area, produced a successful diversified economy. In 1980 the number of business establishments totaled 2,388; 25 percent of the population was employed in manufacturing and 23 percent in wholesale and retail trade. Most of the population, 59 percent, worked outside the county. The economic growth between 1960 and 1980 accompanied a comparable population growth. Plano, eighteen miles northeast of Dallas, had the most dramatic increase of all Collin County towns: in 1960 Plano's population was 3,695, and twenty years later it was 72,331. Overall, Collin County's population increased from 41,692 in 1960 to 144,576 in 1980. Subsequently it continued to grow, largely as a result of the development of the suburbs in and around Plano. By 1990 the number of residents in Plano increased to 128,673, and the population of the county as a whole grew to 264,036, nearly double what it had been only a decade before. Many of the new arrivals in the county are from areas outside of Texas. As of 2014, the population of the county was 885,241, and the population of Plano was 278,495.
Though before 1970 the voters of the county were staunchly Democratic, from 1972 to 1992 they consistently chose Republican presidential candidates, and Republicans also made inroads in state and local races. Other changes have occurred. Due to the large number of young families that have moved to the area, the average age has dropped considerably, and education levels have been steadily rising. Hispanics, traditionally only a small minority in the county, now outnumber African Americans, and the number of Asians is increasing rapidly. In 2014 about 61.2 percent of the population was Anglo, 15 percent Hispanic, 9.4 percent African American, and 12.3 percent Asian. Collin County is well on its way to being one of the most densely populated counties in Texas. The largest city, Plano, overshadows the county seat as the business and educational center of the county. The diversified economy continues to diminish the number of farms. At its 150th anniversary the county little resembled what was settled in the 1840s.