Douglas' Battalion, Tennessee Partisan Rangers
"Organized October 1862; companies never lettered; the companies were variously assigned to other organizations, and four remaining companies were consolidated February 25, 1863 with Holman's Partisan Ranger Battalion, to form 11th Tennessee Cavalry Regiment." 
"Units of the Confederate States Army" by Joseph H. Crute, Jr. contains no history for this unit. 
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.
"No muster rolls of the battalion were found, and the information given below was taken from the records of the organizations to which the companies were later assigned.
- John Lytle. Organized October 4, 1862 at Salem, Rutherford County. Became Company "D", 11th Regiment.
- Chatham Coffee. Organized September 15, 1862 from Coffee and Warren Counties. Became Company "H", 11th Regiment.
- Thomas F. Perkins. Organized August 10, 1862 at Franklin, Williamson County. Some men from Davidson County. Became Company "I", 11th Regiment.
- 0. F. Bruster or Brewster. Organized July 28, 1862 at McMinnville, Warren County. Became Company "L", 11th Regiment.
- T. C. H. Miller. Organized October 28, 1862 at Chapel Hill, Marshall County. Operated with, but not a member of the battalion.
- James B. Harvey. Organized May, 1862. Became Company "F", 2nd (Woodward's) Kentucky Cavalry Regiment.
- Nathan W. Carter. Organized September, 1862 at LaVergne, Tennessee with men from Davidson and Rutherford Counties. Became Captain Carter's Company Independent Scouts; later Company "A", 21st Tennessee Cavalry Regiment.
- Richard McCann. Organized September, 1862. Became Company "K", 9th Tennessee Cavalry Regiment. McCann was from Nashville, and the company was probably from Davidson County. It was attached to the battalion for only a very short time.
- Felix H. Blackman. Men from Davidson County. Became Company "I", 9th Tennessee Cavalry Regiment. It was attached to the battalion for a very short time.
No muster rolls were found for McCann's or Blackman's Companies." 
- Beginning United States Civil War Research gives steps for finding information about a Civil War soldier or sailor. It covers the major records that should be used. Additional records are described in 'Tennessee in the Civil War' and 'United States Civil War, 1861 to 1865' (see below).
- National Park Service, The Civil War Soldiers and Sailors System, is searchable by soldier's name and state. It contains basic facts about soldiers on both sides of the Civil War, a list of regiments, descriptions of significant battles, sources of the information, and suggestions for where to find additional information.
- Tennessee in the Civil War describes many Confederate and Union sources, specifically for Tennessee, and how to find them.. These include compiled service records, pension records, rosters, cemetery records, Internet databases, published books, etc.
- United States Civil War, 1861 to 1865 describes and explains United States and Confederate States records, rather than state records, and how to find them. These include veterans’ censuses, compiled service records, pension records, rosters, cemetery records, Internet databases, published books, etc.
- Tennesseans in the Civil War, Doulgass' Tennessee Partisan Ranger Battalion, (accessed 25 Apr 2012). A brief history.
- fold3$, Cox's Battalion and Douglass' Battalion and Partisan Rangers and Greer's Regiment Partisan Rangers and Holman's Battalion, Partisan Rangers, (accessed 25 Apr 2012). Unit information and rosters.