Clint Smith at The Paris Review:
The Emancipation Proclamation, some forget, was not the sweeping, all-encompassing document that it is often remembered as. It applied only to the eleven Confederate states and did not include the border states that had remained loyal to the U.S., where it was still legal to own enslaved people. Despite the order of the proclamation, Texas was one of the Confederate states that ignored what it demanded. And even though many enslaved people escaped behind Union lines and enlisted in the Federal Army themselves, enslavers throughout the Confederacy continued to hold Black people in bondage throughout the rest of the war. General Lee surrendered on April 9, 1865, in Appomattox County, Virginia, effectively signaling that the Confederacy had lost the war, but many enslavers in Texas did not share this news with their human property. It was on June 19, 1865, soon after arriving in Galveston, that Granger issued the announcement, known as General Order Number 3, that all slaves were free and word began to spread throughout Texas, from plantation to plantation, farmstead to farmstead, person to person.
more here.