President Abraham Lincoln proclaimed the freedom of slaves in the states that were in rebellion against the federal government on January 1, 1863. This included, of course, the State of Texas. The war was ongoing, though, and where Union forces did not know of it or did not press it, it had no practical force. There were particularly few effective Union forces in Texas before 1865.
An East Texas newspaper has been found with a story about Lee's surrender to Grant in April 1865. The rebel army of the Trans-Mississippi didn't surrender until June 2, 1865. It wasn't until June 18, 1865 that Union General Gordon Granger came to Galveston, then Texas's largest city, with 2,000 troops to occupy Texas, and the next day, June 19, 1865, he read General Order Number Three from the front balcony of Ashton Villa, which freed Galveston's slaves and proclaimed liberty to the captives of the Lone Star State.