That is not quite right. Juneteenth celebrates the day that it was announced in Texas that slaves in the defeated Confederate States of America had been freed.
The United States clung to slavery until passage of the 13th amendment which occurred later.
It is interesting to note that according to official records Virginia ratified the 13th amendment before Ohio; Louisiana before Minnesota; Arkansas before Connecticut; and Georgia before New Jersey.
Slavery did not officially end until the ratification of the 13th amendment on Dec. 6, 1865. The loyal slave states (and occupied areas of the Confederacy as of Jan. 1, 1863) were not covered by the Emancipation Proclamation.