Born Oct. 3, 1846 to Shelby and Elizabeth Cook, the oldest of seven children, Green Berry Cook was raised in Hempstead, (Waller Co., Texas) as a boy.
In 1862, at the age of 17, he enlisted as a paid substitute for J. M. Harrison at Camp Roger in Mansfield, Louisiana, joining the Confederate Army as a Private with Co. A, 18th Texas Infantry. (The Company had first formed at Camp Grace in Hempstead Texas.) When he turned 18, he enlisted on his own behalf.
Serving under Major General John G. Walker, who took command of a Division of Texans, that was later know as Walker's Greyhound Division. The Division was known for their ability to march rapidly in good order and they showed excellent service at Mansfield, Louisiana (Apr. 8, 1864) and at Pleasant Hill (Apr. 9, 1864).