Who made these chairs?  

I think...
They are Risom, just early?

No, not Risom.
Compare the armless chair above to the Risom chair below. Note the Risom's details: the triangular seat sides, the one-piece stile and rear leg, the leg-to-seat angles, etc. The armchair above is even further removed from Risom's design.

There is a thread about...
There is a thread about these chairs from a couple of years ago, I can't seem to locate. I have the same chair and have still not been able to find the maker.

While this doesn't answer...
While this doesn't answer your question, here is a quick video from DWR of a Risom interview, where he talks about the chair design, and it's subsequent copies.
http://www.youtube.com/watch?v=JcsbU532VFw

If it helps.... these chairs...
If it helps.... these chairs belonged to the current owners parents. She grew up in a wealthy suburb of New York City and I believe they were purchased in that area. They were in her fathers law firm. I am a wood worker with the task of salvaging these chairs. The pics above are the worst of the lot. I like the walnut/leather combo, it gives the chair a different feel from the Risom version. The back legs could be considered a cheaper way to construct the chair, but it helps streamline the design. Thanks for the input.

I purchased my chair in...
I purchased my chair in Eastern Long Island......so maybe they were produced regionally?