Over 5% of the population of Hesse Cassel was "under arms" at this time; I might be wrong, but I have a feeling that they did the same thing as the Brunswickers and split their regiments in half, sending one battalion from each to America.
Only Prussia had a higher percentage in uniform (described as not so much a nation with its own army, as an army with its own nation), but they did it by recruiting non-Prussians and kidnapping foreigners who were daft enough to be "passing through" when it got dark. Great Britain and Ireland, by comparison had approximately 0.5% in uniform (40,000 Regulars in a population of c.8 million in the 1770s); of course The Andrew took a much bigger chunk of the male populace.