There is written a biography of Oklahoma Sherriff Edward R. Young from Coosa County served in the 18th Alabama with his six brothers and later in Wheeler's Cavalry (which would include Forrest's commands). There is also mentioned a McDonald's Company in Coosa County and a Coosa County Volunteer Cavalry Company (1859-60).
All of this, along with Evelyn's first post, is vague enough for the possibility to put SOMEBODY from Coosa County, Alabama in a Confederate cavalry command called "McDonald's". More needs to dug up.
David