History of Marion County 1881 pg 931 refers to this unit. A Capt. Poindexter led men from Marion County in a company at Wilson's creek. Listed as Co A, Col JM Majors' Battalion of Cavalry, John B Clark's Brigade (3rd division I think)
There is an additional listing of a JP Watson in the SOS file that was also part of Capt. Poindexter's Co A having been with the unit at Carthage and Wilson's Creek, again cavalry. This is documented in History of NE Missouri Vol 3, pg 1613. All these entries for service in 1861. The Watson entry states he ended up furloughed at Lexington 1.
So at least one company cavalry raised, was at Carthage and Wilson's Creek. Appears under Clark's command 3rd Div MSG.
Side note the Marion county history has a significant 2nd division officers MSG roster from NE Missouri. Starts on pg 932.