https://chroniclingamerica.loc.gov/lccn/sn84024283/1918-05-02/ed-1/seq-1/

Birth of a Nation - "The World's Greatest War Picture!" - is playing in Ironton, Missouri, both in the afternoon and evening of May 4. The $500,000 in production costs, employment of 18,000, use of 3,000 horses and wild rides of the Ku Klux Klan are noted. The popularity of the movie has limited it to the largest cities until this point.

Source: "The World's Greatest War Picture," Iron County Register, May 2, 1918. Page 1, Column 1.