You can argue about whether is a good test or not. Obviously the closer we get to Secession, the more the raising of the company is attributed to anticipated confederate service, but I don’t know of another way to draw a “Bright Line”.
The Volunteer Militia Companies were not technically a part of the local militia regiment. The Militia Law of 1860 really sets them apart from the standard militia. Compare Section 1 of the Militia Law, to Section 57-60 for the difference between the regular militia and the Volunteer Companies.
When you examine most of the Militia Regiments in the “List of Commissioned Officers of the Militia 1827–1862” you find a list of line companies for the regiment, and then the Volunteer Company, if one existed, listed separately. In Jefferson County, 24th Militia, Regiment, I only find the following Companies listed:
Date Officer Unit
14 Nov 60, Thomas A. Loman, Jefferson Guards,
4 Dec 60, Samuel Taylor, Company H, 2nd Battalion
18 Dec 60, Joseph W. Bocage, Southern Guards,
15 Mar 61, Lewis Reed, Company A, 1st Battalion
5 April 61, Bernard Fitzpatrick, Company C, 2nd Battalion.
20 April 61, John Ashcraft, Company I??, 2nd Battalion
20 April 61, Fredrick Steek, Pine Bluff Artillery
25 May 61, ?? Reudooff, Volunteer Home Guard Arty
17 June 61, J.H. Bradley, Bradley Guards
24 July 61, George W. Baynes, McCulloh Guards
24 July 61, R.H. Wallace, Arkansas Travelers
1 Aug 61, James H. Hacoly, Bradley Guards
There are additional officers listed for most of these units, but I have only listed one for each. My photo copy only goes through August of 61.