It's a mystery to me too why so-o-o-o many Matchett's live in the same county during the mid-1800's !My family consists of J. L. Matchett who married Margarret J. Knowles (1829-1904) and resided in Wash. Co., TX.Their daughter, Sarah Lilie Matchett (1863-1962) is my G-g-grandmother from Brenham, TX. Her siblings were Margaret Katherine (1861-1935), Emma, Fannin, and twin boys both Tom & Jake.
As for other Matchett's in the area, here's my list off the Texas census: Mary Ballard Matchett (1835-1921) Russell Maynard Matchett (1874-1889) S. Annie Jameson Matchett (1872-1947) T. D. Matchett (1826-1901)/ Co. A 3rd TX inf. Willie Spivey Matchett (1869-1894) Eula Perry Matchett (1872-1884)
These might be kin to my family or yours but the link is a mystery.Hope this will help in your search endeavors. . .