Were you aware that militia were all free white able-bodied males aged roughly 16-60 (varies by time and place) within a given County?Each such person was expected to turn out for regular drills (lists of who turned up constitute a large part of surviving rosters; those who did not were subject to a fine, so the County Court was interested in collecting such records).These musters were not considered active duty.
Each such person was expected to be available should there be reason to activate the militia for defense within the County, or to perform other tasks such as assisting escort of supplies bound elsewhere, patrolling, guarding prisoners.
In VA the Companies were mostly geographically based.The County Court determined what the geographical division for a given Company would be, but the State Legislature determined how many Companies there would be, configurations of officers, regulations, etc., and both Legislature and Governor approved appointment of commissioned officers who were nominated by the County Courts.A very useful possible resource in this light is William Waller Hening's _Statutes At Large_.The inestimably generous Freddie Spradlin has been transcribing and uploading these volumes:
Praying for survival of County Court records for this period, you might find specific descriptions of Company geographic districts in the Court records, records of nominations of officers (or of elections of officers by members of companies, which were considered recommendations not final-selections), promotions to replace persons who died or resigned or were removed, etc.These records might also include disbursement from the levies to individuals for active-duty service, for losses while in service and other useful bits.A wife might apply to the County Court or to the Overseers of the Poor for subsistence while a husband was away.These records can only be investigated in person.
These militia districts generally were also tax districts.The surviving 1782 and 1784 tax lists were organized usually by district, but sometimes the copies sent to the Library of VA were recopied in alphabetical order.Not all survive.The 1782 list for Mecklenberg does survive.The National Archives has a transcript in a file, 1790m-02.pdf that you can download here:
If you have done any cluster research and investigated the land grants at Library of Virginia, you can get an idea of where in the County your people lived, who their neighbors (and likely kin and friends/enemies) were and such.These lists can be useful for differentiating between similarly-named people, but you also need to investigate deeds, other tax lists (such as the Land Books), estate records and so forth.