There are multiple sources of information that can be used to identify possible camp sites. The Official Records are a very valuable resource, but many other resources are available on line, including Regimental histories, soldiers diaries, letters, maps and period newspapers.
I am researching all of the military traffic that passed through Gibson County located in West Tennessee. The junction of the Mobile & Ohio and Memphis & Ohio railroads occurred at Humboldt, a small town in the southern end of the county. The Mobile & Ohio was an important railroad for many of the major military campaigns. The railroads in Gibson County were the focus of Gen. Nathan Bedford Forrest's two raids in West Tennessee. Forrest's damage to the railroads and the disruption it caused to the flow of Union men and materials to the south, were one factor in Gen. Sherman's decision to "live off the land" on his march to the sea through Georgia.
Here is an example of some of the information I have gleaned from various sources. The withdrawal of Gen. Polk's Confederate forces from Columbus, KY in the spring of 1862 followed the line of the Mobile & Ohio south to Corinth, Mississippi. Union forces then advanced along the same railroad, repairing it as they moved south. One of the advance guard units was the 7th KS Cavalry (Jennison's Jayhawker's) whose jayhawking activities first used during the Kansas-Missouri border wars, became accepted Union army behavior. Col. Daniel Anthony, brother of the famous Susan B. Anthony, was in command of the regiment as it advanced south from KY into TN. This regiment was attached to Gen. Robert Mitchel's brigade tasked with repairing the railroad damaged by the Confederates as they retreated south from Columbus, KY.
On June 10, 1862, Anthony wrote a letter from Camp Etheridge, TN. He detailed his regiments movements from Leavenworth, KS through Columbus, KY into TN. On June 20th, he wrote another letter from Camp Etheridge describing it as near Dresden, TN. The official records note that Gen. Mitchell's brigade camped on a near Union, TN on a farm belonging to the mother of Hon. Emerson Etheridge.
Emerson Etheridge was a lawyer from Dresden, TN, who had been a two term Congressman from TN and was a staunch Unionist. In April of 1861, Etheridge made a speech at Trenton described by Robert Johnson, son of Andrew Johnson, Lincoln's later Vice-President, that he described as "the most bitter speech ever heard to fall from the lips of man". When Etheridge attempted to speak later at Paris, TN, it caused a riot. At the time of that Gen. Mitchell's forces were camping on his mother's farm, Etheridge was the Clerk of the House of Representatives in Washington, DC.
There is no doubt that Camp Etheridge was located on or near the farm of Etheridge's mother. An April 10, 1862 issue of the Davenport, Iowa "Davenport Daily Dispatch" noted that Etheridge's residence was located 35 miles southwest of Hickman, KY. Federal Population census records document that Etheridge's father and mother resided in the Civil District located at the southwestern corner of Weakley Co., TN. Etheridge is buried in a cemetery located along the road which connects Dresden to Kenton, TN, which was one of the stations along the Mobile & Ohio Railroad. The camp on this farm would have had easy access to the railroad. The Etheridge farm lay somewhere along this road. Further research into County deed records could better approximate the location of this farm. Due to the number of troops that camped there, it might be a site worth investigating.