When was the first Juneteenth marked in the US?

Question

11 November is marked in many countries as Remembrance Day, Poppy Day, Armistice Day or Veterans Day to commemorate the sacrifices of members of the armed forces and civilians in time of war. Why has that date been selected?

Answer 1

19 June 1866
The first celebration was the year after abolition of slavery was announced by the Union Army commander in Texas.