The U.S.A. considered Missouri a Union State, the C.S.A. considered it a Confederate State, but I personally consider it far too divided to list it for either side. It definitely was one state that earned the "border state" title.
A few things to keep in mind in regards to the numbers of men Missouri sent to each side, along with the guerrillas you mention the numbers of the M.S.G. should also be considered, whose strength taken at one specific time is estimated to have peaked at 28,000 - with 40,000 Missourians estimated to have served in it by the wars end. Even considering recruiting parties sent behind Union lines throughout the war, the Confederate source of recruits from the "Little Dixie" region was cut off from easy access quickly by Lyon. There was also the conscript law requiring all citizens eligible for military service to enroll in the Union E.M.M. It is hard to say how many were conscripted that would not have joined otherwise, but it is something to keep in mind.