Was just reading a thread on this on Cloudy Nights the other day. Not made in the US. Some in Japan and some in China. I'll find the thread and post below.
Here it is:-
http://www.cloudynights.com/ubbthrea.../o/all/fpart/1
In summary:-
"Nagler Zoom, Plossls and Type 6 Naglers are made in Japan. The rest are made in Taiwan ROC."