Hi Lynn. In my Blacker surname data base, I have 3 other Blackers beside your Robert & his son Robert Lee (seems he went mostly by R.L.)located in Logan Cty. Ill. These 3 are female: Annie E. [Blacker] Ashhurst m.1885 & E.B. [Blacker] Ragen m.1887 & Harriet [Blacker] Hogbin m.1866. It is possible one is a sister, locating siblings can help in finding parentage. You mention Robert was born in Ohio.. a possible lead for you is Robert Blacker III/b.1833 in Butler Cty, Ohio/parentage:Robert II & Anna (Abraham) m.1820 in Butler Cty, Ohio. I have some source info on Robert II, including naturalization papers [Co. Armagh, Ire] other possible parentage is Robert A. & Mahala [Clay] m. 1837 in Ross Cty, Ohio They had a son named Robert b. abt 1838... many descendants of this line are found in McLean & Piatte Cty. Ill. I have lg amount of data.Good luck!