Texas counties are based on Spanish law and the history of Texas. Under Spanish and Mexican rule, Texas was divided into municipalities (municipalities in Spanish). When the Republic of Texas gained independence in 1836, the 23 municipalities became the first counties in Texas. Counties are created by the Texas Legislature.
They are considered legally organized after a county seat has been established and a court of commissioners has been elected and established. Rockwall County was created from Kaufman County in 1873 due to poor access to the former seat of Kaufman County and is the smallest county in Texas, with 149 square miles. After the establishment of the Republic of Texas and its new government following the revolution against Mexico, the boundaries of existing municipalities as new counties were vague and not well defined. Counties formed from those already organized had to be at least 700 square miles in size and no parent county could be reduced to less than that minimum.
In the early days of the state, Texas became a state in 1845, Texans needed to be close to local governments, which were responsible for courts, jails, schools and highways, said attorney David Brooks, who specializes in Texas county government. The rules changed once again after Texas became a state in 1845, when the new Texas Constitution stipulated that no existing county could be reduced to less than 900 square miles without the consent of a two-thirds majority of the Legislature. Brewster County in West Texas is the largest at 5,935 square miles, three times the size of Delaware and more than 500 square miles larger than Connecticut. When Texas sold land to the United States as part of the Compromise of 1850, nine other counties were added.
In some cases, the Republic or later the State of Texas imposed the name of the new county, while in others, no one knows with certainty how the county got its name. At least 32 counties established by Texas law no longer exist, since they disappeared due to changes in the Texas constitution, and were eliminated because of their designation as judicial counties or because of political party disputes during the Reconstruction after the Civil War. The Constitution of 1876, which is what much of today's Texas state legislation is based on, established requirements for Texas counties. During 1876, the Texas Legislature created 4 new counties in the Panhandle and the lower plains of West Texas in anticipation of growth as railroad construction spread throughout the region and had an almost square boundary configuration.
In 1876, a new Texas Constitution stated that new counties of less than 900 square miles could not be formed from unorganized land, and that these counties should be as square as possible. The first counties in Texas history were called municipalities and date back to Spanish rule, according to the Texas Association of Counties. The Congress of the Republic of Texas established Bowie County to include the entire region that stretched from Texarkana to Wichita Falls and from the Red River south to Longview in a north-south direction.