Lincoln issued the preliminary Emancipation Proclamation in the midst of the Civil War on September 22, 1862, declaring that if the rebels did not end the fighting and rejoin the Union, all slaves in the Confederacy would be freed on the first day of the following year.  On January 1, 1863, Lincoln issued the final Emancipation Proclamation, declaring that all slaves in the Confederate States of America in rebellion and not in Union hands were freed.

More isolated geographically, planters and other slaveholders had migrated into Texas from eastern states to escape the fighting, and many brought slaves with them, increasing by the thousands the enslaved population in the state at the end of the Civil War. Although most lived in rural areas, more than 1,000 resided in both Galveston and Houston by 1860, with several hundred in other large towns. By 1865, there were an estimated 250,000 slaves in Texas.

Enforcement of the Proclamation generally relied upon the advance of Union troops. Texas, as the most remote state of the former Confederacy, had seen an expansion of slavery because the presence of Union troops was low as the Civil War ended.  Despite the surrender of Confederate General-in-Chief Robert E. Lee at Appomattox Court House on April 9, 1865, the western Confederate Army of the Trans-Mississippi did not surrender until June 2.  On the morning of June 19, 1865, Union Major General Gordon Granger arrived on the island of Galveston^] to take command of the more than 2,000 federal troops recently landed in the department of Texas to enforce the emancipation of its slaves and oversee Reconstruction, nullifying all laws passed within Texas during the war by Confederate lawmakers. The order informed all Texans that, in accordance with a Proclamation from the Executive of the United States, all slaves were free:

“The people of Texas are informed that, in accordance with a proclamation from the Executive of the United States, all slaves are free. This involves an absolute equality of personal rights and rights of property between former masters and slaves, and the connection heretofore existing between them becomes that between employer and hired labor. The freedmen are advised to remain quietly at their present homes and work for wages. They are informed that they will not be allowed to collect at military posts and that they will not be supported in idleness either there or elsewhere.”

Longstanding urban legend places the historic reading of General Order No. 3 at Ashton Villa; however, no historical evidence supports such claims. Although widely believed, it is unlikely that Granger or his troops proclaimed the Ordinance by reading it aloud: it is more likely that copies of the Ordinance were posted in public places, including the Negro Church on Broadway, since renamed Reedy Chapel A.M.E. Church.  Although this event has come to be celebrated as the end of slavery, emancipation for the remaining enslaved in two Union Border States (Delaware and Kentucky), would not come until several months later, on December 18, 1865, when the Thirteenth Amendment was ratified. 

Former slaves in Galveston rejoiced after General Order No. 3. One year later, on June 19, 1866, freedmen in Texas organized the first of what became annual commemorations of "Jubilee Day". Early celebrations were used as political rallies to give voting instructions to newly freed African Americans. Other independence observances occurred on January 1 or 4.

In some cities, Black people were barred from using public parks because of state-sponsored segregation of facilities. Across parts of Texas, freed people pooled their funds to purchase land to hold their celebrations. In 1872, Black leaders in Texas raised $1,000 for the purchase of 10 acres of land, today known as Houston's Emancipation Park, to celebrate Juneteenth.  The observation was soon drawing thousands of attendees across Texas. The Black community began using the word Juneteenth for Jubilee Day early in the 1890s. The Current Issue, a Texas periodical, used the word as early as 1909, and that year a book on San Antonio remarked, with condescension, on "June 'teenth'".

In the late 1970s, when the Texas Legislature declared Juneteenth a "holiday of significance ... particularly to the blacks of Texas”, it became the first state to establish Juneteenth as a state holiday. The bill passed through the Texas Legislature in 1979 and was officially made a state holiday on January 1, 1980. Before 2000, three more states officially observed the day, and over the next two decades it was recognized as an official observance in all states, except South Dakota, until becoming a federal holiday on June 17, 2021. In New York, it was first officially observed in 2004, but did not become a paid state holiday until 2020.