Col George Washington McKenzie
McKenzie's Fighting 5th
Picture taken about 1878-1893 in Decatur in front of courthouse with 26th TN flag and other people & regiments.  
Brief History
This regiment was organized in December, 1862, using the 13th Tennessee Cavalry Battalion as its nucleus. The regiment surrendered with the Army of Tennessee. [1]

"...designated as 5th (McKenzie's) Cavalry Regiment.  It was also known as the
1st (Rogers') East Tennessee Cavalry Regiment, 2nd (MeLin's) Tennessee Cavalry Regiment, 2nd Tennessee Cavalry Battalion, and the 13th Tennessee Cavalry Battalion." [2]

Companies in this Regiment with the Counties of Origin
Men often enlisted in a company recruited in the counties where they lived though not always. After many battles, companies might be combined because so many men were killed or wounded. However if you are unsure which company your ancestor was in, try the company recruited in his county first.

Company A - Captain J.L. Blackwell
Company B - Captain James M. Kincaid, John Blythe
Company C - Company W.O. Martin, D.C. Blevins
Company D - Captain A.W. Beagles
Company E - Captain Thad. M. Carder
Company F - Captain Thomas Gorman, A.L. Mims
Company G - Captain John W. Graham
Company H - Captain William W. Mullendore
Company I - Captain William W. Lillard
Company K - Captain Dewitt C. GhormleyLinks:

https://familysearch.org/wiki/en/5th_Regiment,_Tennessee_Cavalry_(McKenzie's)_(Confederate)
http://www.mountainpress.com/books/tn/details/tn-1153w.