According to the American Religion Data Archive, in the year 2000
there were 250,402 of what I would call mainstream 'congregations' in
the US, out of a total of 268,254 all told.
The vast majority of these are Christian demoninations. There are
3,727 Jewish congregations included, and 1,209 Muslim congregations.
You can find the full list yourself, broken down by affiliation, at the ARDA site:
From the pull-down menu near the top of the page, select [ Maps/Report
] and then choose the report for the entire country (unless, of
course, you want to see statistics for individual states, etc).
As is the case with any national statistics, you should take these
numbers with the appropriate grains of salt. The site does a good job
of discussing how the data were compiled, and what might be missing
from the numbers...I would encourage you to have a look.
I trust this information fully answers your question.
However, please don't rate this answer until you have everything you
need. If there's anything more I can do for you, just post a Request
for Clarification, and I'm happy to assist you further.
search strategy -- Used bookmarked sites for religion statistics.