Generally men enlisted in their home county companies, but it was not unusual to find them in adjoining county units. You are probably aware Pike and Lawrence Counties are neighboring counties today and were more so prior to the formation of Lincoln County in 1870.
Jasper Newman was enrolled in state service as a private in the Bogue Chitto Guards on April 27, 1861 by Captain R. S. Carter at Bogue Chitto. He was mustered into state service May 1, 1861 by Captain R. J. Bowen also at Bogue Chitto. This was the extent of his service in what became Company B / 7th. Miss. Infantry Regiment.
Apparently he received a transfer, but is noted as AWOL from the 7th. Miss. on June 5, 1861 -- left with Captain W. C. Brooks Company known as Stevens Rifles for the war.
(By this date, June 5, 1861, Captain Brooks' Company was in Virginia)
Captain W. C. F. Brooks' Company (Stevens Rifles/Stephens Rifles/Stephens Guards) became Company C/21st. Miss. Infantry Regiment. A capsule history of this regiment is available at this site. http://mississippiscv.org/MS_Units/21st_MS_INF.htm
There are service records available for a J. (John) N. Newman (age 18 in 1861) in Company C/21st. Miss. at this link.
Hope this helps,