From NKAA, Notable Kentucky African Americans Database (main entry)
Washington, Isam McDaniel "Mack"
(born: 1875 - died: 1957)Isam [or Isom] M. Washington was born in Lovelaceville, KY, the youngest son of Rebecca Neal Washington and Isam Washington. Isam married Arbella Weeks from Massac County, IL; they were the parents of Roy L. Washington and the grandparents of Chicago Mayor Harold Washington.
Isam was a minister at several churches in Illinois; he helped raise funds for the building of the St. James Church in Lawrenceville and the St. Peter A.M.E. Church in Decatur.
For more see The Ancestry of Mayor Harold Washington (1922-1987), by C. G. Brasfield.