I may have just found a useful clue in the DAR application I mentioned in an earlier post. It refers to something called "Manuscripts of Colony and State of New York in the Revolutionary War". It looks like it has the following references for William Yerks.
Volume 13, folio 55
Volume 16, Folio 180 Pension Papers
Volume 42, Folio 70, page 12
Volume 50, Folio 93, page 3
I could not find an exact match for this, but....
It also mentions...
"Robert's New York In The Revolution, page 266 or 286
I did find "New York in the Revolution as Colony and State", by James Arthur Roberts on Google Books. It does mention a William Yerkis on page 226.http://books.google.com/books?id=1JMLAAAAIAAJ&printsec=f...
Anybody have any idea what the actual name of "Manuscripts of Colony and State of New York in the Revolutionary War" is and/or where I can find it?