Bob, the source of the information about John Mill growing cranberries was from a State Board of Agriculture report from 1874, which I found on a Burlington Library System web site. Scroll down to the third heading on the right THE WILD BERRY IS TAMED.
http://www.burlco.lib.nj.us/pinelands/cranber.htm
The other source, that claims Burlington County had the first cranberry bog in New Jersey, was a sort of anonymous web site. Either the site didn't bother to list the original source or it is just a case of some wishful thinking on the part of some overzelous cranberry farm/ Burlington County promoters. After all, most of the cranberry farms are in Burlington County. Maybe some interested party could do some further historical research. To me, it's not that important to document who was the first. At least I wouldn't go to great lengths to find out.