The first time was in 1845. December 29th. Then, of course, there was that messy business known as the Civil War. Texas seceded from the Union over the course of the first part of 1861 and joined the Confederacy. Readmission seems to have been a gradual process. "When the war ended in April 1865, Texas was still considered to be in revolt (the last battle of the Civil War was fought on Texas soil after the surrender at Appomattox). Although a state of peace was declared as existing between the United States and the other Southern States on April 2, 1866, President Andrew Johnson did not issue a similar proclamation of peace between the U.S. and Texas until August 20, 1866, even though the Constitutional Convention of 1866 had approved on March 15, 1866 an ordinance to nullify the actions of the Secession Convention Southern States remained under military government until their legislatures adopted the 13th, 14th, and 15th amendments to the United States Constitution. Their readmission to full national status varied from state to state (Georgia was readmitted twice). In April 1869, the U.S. Congress passed an Act authorizing voters of Virginia, Mississippi and Texas to vote on their new state constitutions and to elect state officers and Members of Congress. Three months later, President U.S. Grant signed a proclamation submitting the Texas Constitution to the voters of the state." There's more, and it can be found at: http://www.tsl.state.tx.us/ref/abouttx/secession/index.html