Information from Kaiyu, a Chinese clarinetist:
And Jupite clarinet is made in Taiwan of China and some lower level models are also made in China. It is not a small company.
Here is the link.
Skip the graphic by clicking on the upper right, and click on Clarinet for a list of models and specifications.

This information is from Annette in Canada. Thanks, Annette!
I suspect that the main market for Jupiter clarinets here is to sell as band instruments for public and high school students.  Our local store here (the only one that sells clarinets) retails the Jupiter 631 (plastic) clarinet for just over $600 CAN.  Having said that, most of the band programs in our city rent instruments from Long and McQuade Musical Instruments in Toronto.  I had the opportunity to try the Jupiter 931S Parisienne clarinet on a visit to Ottawa last year.  This is their top of the line clarinet and was selling for just over $900 CAN.  I thought the intonation was excellent, the response even and tone pleasant.  It seemed to be a little more free-blowing then the clarinets I usually play (my personal preference is for a bit more resistance). The keywork was comparable to that found on a mainline intermediate clarinet (such as the Buffet E-11), certainly acceptable but probably not as heavy and durable as some.  I didn't look at the details of the clarinet's construction, but overall I'm guessing the Parisienne would be a good alternative as an intermediate instrument.

Attached below is a scan of the Jupiter catalogue, from Annette in Canada. The catalogue lists there models, including bore diameters and other details, and gives a few words of history for the company.
Subpages (1): Jupiter 631 II
Phil Pedler,
Dec 21, 2010, 8:23 PM