According to the map showing the dispersion of the Missouri State Guard assets on page 23 of "Price's Lieutenants" Texas County falls into the area of the 7th Division.
I also took the liberty of looking up the military service records of George W. and Jasper Cox in the online MO State Archives at the MO Sec'y of State's Office website at http://www.sos.mo.gov/archives/soldiers and found nothing about the cousins' service in the MSG. The MO State Archives southerners' records are very incomplete.
I did find cards for both George W. and Jasper Cox that told me:
--both enlisted in Company B, 8th Infantry Regiment (Mitchell's)(Confederate) at Eleven Points Mill;
--George surrendered at New Orleans 26 May 1865 while in Company I, 8th MO Infantry, and was paroled at Alexandria, LA 7 Jun2 1865;
--George was a private and Jasper was a sergeant in Company B, 8th Infantry Regt;
--postwar George attended reunions as a member of General James McBride's camp # 787 U.C.V. at Houston, MO.
I hope that helps.