There were four Alabama companies in the 40th Tennessee Infantry Regiment. These were:

Co. A -- Capt. Hiram A. Higgins, Limestone County
Co. E -- Capt. G. W. Whitfield, Limestone & Morgan Counties
Co. H -- Capt. John A. Minter, Coffee & Dale Counties
Co. K -- Capt. Aaron G. Hammack, DeKalb County

Co. D of the 4th Confederate was also from Coffee County. All of these companies were later assigned to the 54th Alabama. I don't see the McMillan name you mentioned among the captains of this command.