Who started calling it Juneteenth?

Blacks 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'”.

When did they start calling Juneteenth?

Freedom finally came on June 19, 1865, when some 2,000 Union troops arrived in Galveston Bay, Texas. The army announced that the more than 250,000 enslaved black people in the state, were free by executive decree. This day came to be known as “Juneteenth,” by the newly freed people in Texas.