According to Civil War Washington and an official petition for freedom from slavery, Osbourn Dorsey was "about eight months" old on May 19, 1862. This means his estimated birth date is around Sept. 19, 1862, but the exact date is not known.
Dorsey was a black inventor who received patent #210,764 for a door holding and closing device on Dec. 10, 1878. The first documented doorknob patent was issued the same year. According to About.com, other black inventors around Dorsey's time were James Henry Dunnington, who received a patent for a horse detacher on Mar. 16, 1897, and Phillip Downing, who received a patent for a street railway switch on June 17, 1890 and two separate patents for a letter box on Oct. 27, 1891.