Evidently multiple William Coopers lived in colonial Texas. Two of them were members of Stephen F. Austin's Old Three Hundred. Though it is impossible to sort the biographical facts about these two men with any final confidence, one of them was associated with Matagorda County and the other with Waller and Austin counties. On August 10, 1824, the latter received title to 1½ sitios of land in what is now Waller County and two labors of land now part of Austin County. He was probably the man classified in the 1826 census as a farmer and stock raiser, aged between forty and fifty, with a household including his wife, aged between twenty-five and forty, three sons (the oldest between sixteen and twenty-five), two daughters, two servants, and three slaves. Though the evidence is far from conclusive, he was probably the "Cow" Cooper who with his wife, Sarah (James) of South Carolina, immigrated to Texas from Tennessee in 1822. They eventually settled near San Felipe, where he reportedly ran a small store and owned a large number of cattle. A small collection of the papers of this William Cooper is housed at the Barker Texas History Center. He was probably the "Cow" Cooper whose stock ranch was located on the east side of the Brazos River below San Felipe, though "Cow" was also the nickname of a Cooper who came to Texas from Miller County, Arkansas, possibly with Henry Jones and William Rabb, sometime before November 1822.
Also, by 1828 or 1829 a "Sawmill" Cooper, evidently another man, was running a store in San Felipe with a partner called Cheves, probably Henry Cheves or Chevis. This may have been the William Cooper above. Evidently "Sawmill" Cooper received his nickname from having worked in the lumber business; one account claims he was mangled while working at a sawmill. The William Cooper who, with partner Moses Morrison on July 24, 1824, received a sitio of land in what is now Matagorda County was probably the man listed in the 1825 census of the Colorado district and classified in the 1826 census as a farmer and stock raiser, a single man aged between twenty-five and forty.
The young William Cooper who was killed about five miles from his parents' residence in a fight with Indians on Caney Creek in November 1830 was probably the son of the Austin colonist "Cow" Cooper. Another son, James Cooper, went with Barzillai Kuykendall to Fort Tenoxtitlán, where he shot off the thumb of one of the Waco Indians who had reportedly killed his brother and then had to hide to avoid capture by Mexican authorities. One of the William Coopers was síndico procurador at San Felipe de Austin in 1829. "Sawmill" Cooper, partner of Henry Cheves, died before January 10, 1832, when the Texas Gazette at San Felipe de Austin carried a notice by J. B. Miller and Henry Cheves, administrators of Cooper's estate. In January 1834 William B. Travis examined the papers of the estate of one William Cooper, possibly the same deceased Cooper whose lands included a half league on the San Bernard River and one at the mouth of Buffalo Bayou. In April 1836 William and Amos Cooper sold several horses to the Texas army on credit and by 1838 still had not received payment; it is possible that this was the remaining Austin colonist.