McKinney was born in Hunterdon County, New Jersey, the second of 10 children born to Daniel and Mercy McKinney. The family moved to Virginia in the 1770s, and while Daniel fought in the American Revolutionary War, Collin McKinney supported the family; thus, he had no formal schooling. After the war, the family moved to an outpost in what is now Lincoln County, Kentucky. McKinney married twice in his lifetime, first to Annie Moore on Feb 10, 1794, with whom he had four children before her death in 1804, and then again in 1805 to Elizabeth Leek, with whom he had seven more children. From 1818 to 1821, McKinney managed the Tennessee estates of Senator George W. Campbell, who was serving as minister to Russia at the time. He also opened a trading post before giving it up and returning to Kentucky. Later, McKinney and many of his relatives moved to Hempstead County, Arkansas, where he was elected as a justice of the peace. In 1826, McKinney became a friend of Benjamin R. Milam, who was recruiting settlers for the Red River Colony in Northeast Texas of Empressario and British General Arthur G. Wavell. The land grant was an area claimed by both the United States settlers as part of Miller County, Arkansas, as well as by Mexico. In 1836, McKinney was one of five delegates from the Red River Colony to the Convention of 1836, which called for Texas to declare its independence from Mexico. He was one of five appointed to draft the Texas Declaration of Independence, and at age 70, he was the oldest to sign it. He later became a member of the committee that drafted the Constitution of the Republic of Texas and also served as a delegate from Red River District and County, Texas, to the First, Second, and Fourth Congresses of the Republic of Texas. In 1846 at age 80, he moved one last time, as a result of one of the worst known floods on the Red River, to the northern portion of the rich blackland prairie of Collin County, Texas, to be near several of his children, although the exact boundary line between Collin and Grayson Counties would not be surveyed and clearly identified for several years. He lived just a few miles southeast of Liberty, Texas, which was soon renamed Mantua by Younger Scott McKinney, who was the founder. Collin McKinney died at his home in Collin County on September 9, 1861, and was buried in the nearby Van Alstyne Cemetery in the McKinney family plot. A historical marker erected by the Texas Historical Commission honors this Texan who lived over 95 years under the flags of four different nations. Around 1873, 12 years after Collin McKinney's death, the few inhabitants of Mantua moved several miles northeast to Van Alstyne, Texas, on the new Houston and Texas Central Railway from Sherman to McKinney and on to Galveston. Today, Mantua is a ghost town of Collin County, with just an old, unmarked cemetery. Both Collin County and McKinney, Texas, its county seat, were named in his honor by the Texas Legislature. McKinney is credited with suggesting to the Texas Legislature that, as new counties were later created in North and West Texas, the boundaries should be about 30 miles square. This would allow a rider to travel to the county seat, conduct necessary business, and return home, all in one day.
