When the election of Abraham Lincoln set off the secession movement with South Carolina and then five other Deep Southern states, Texas opened a convention to consider joining them in leaving the Union. The State Convention opened on January 28th 1861 in Austin, Texas with Oran Roberts as convention president. On February 1st 1861 the convention voted 166 to 8 in favor of the Ordinance of Secession. Texas voters approved the Ordinance on February 23rd 1861, allowing Texas to become a part of the Confederacy by a margin of 46,129 to 14,697.
Texas would go on to send men and equipment to support the Confederate fight. They were also the key to bypassing the Union blockade, using their long border with Mexico for trade; it was sometimes called the “backdoor of the Confederacy”. The last battle to be fought in the Civil War occurred at Palmito Ranch near Brownsville, Texas on May 12th and 13th 1865.
If you would like to read The Texas Ordinance of Secession is a good web site.