I am fairly sure that he was in the von Knyphausen regiment - mustering into New York/Long Island in 1776. What part of Hesse were these troops mostly from? That is the missing link in my research.
In HETRINA, you can apply filters (e.g. "von Knyphausen regiment"/KNY), using "Erweiterte Suche":
https://www.lagis-hessen.de/de/subjects/xsform/sn/hetrina
As a result, you'll get 3562 records. Although Hagen Seehase in "Die hessischen Truppen im Amerikanischen Unabhängigkeitskrieg" mentions no chronological gaps for the "von Knyphausen" regiment data (April 1776 to October 1783, see page 137 in
http://www.vhghessen.de/inhalt/zhg/ZHG_103/Seehase_Unabhaengigkeitskrieg.pdf), the number doesn't match the 6000 soldiers, stated in
Wikipedia (no idea how reliable Wikipedia is in this case).
Scrolling through the results (e.g. by using the arrows), you'll get an impression of the respective Hessian home towns, each displayed on a small map. The soldiers of this regiment, based in
Ziegenhain,
Treysa and Neukirchen (probably this Neukirchen:
https://www.lagis-hessen.de/de/subjects/gsrec/current/3/sn/ol?q=neukirchen), seem to come mainly from the
North of Hesse (i.e. Schwalm-Eder-Kreis, Landkreis Kassel, Werra-Meißner-Kreis, etc.).
As far as Non-Hessians are concerned: Hagen Seehase reports for a bunch of regiments (see page 153), including the regiment "von Knyphausen", a certain portion of soldiers of unknown origin (12%), and quite a lot of "Ausländer" (23%), which means Non-Hessians (see page 157). Altogether, for all troops, the portion of "Ausländer" is reported to be about 21%, very few of them coming from other countries than "Germany" (see page 166).
Apart from that, no further details about the origins of the "von Knyphausen" soldiers are provided. But the "journey" of the regiment is described on page 155/156, including some remarks about captured soldiers, and some numbers of those who returned from captivity. If of interest to you, maybe you might manage to transfer the passage to a translation tool (copy-and-paste works, but unfortunately not very well...).