NoScript does not publish their individual add-on usage statistics, but the global download/usage ratio can be calculated from the statistics on the Firefox Add-on home page:
1,962,617,946 add-ons downloaded
157,090,095 add-ons in use
About 8% of downloaded add-ons are still in use. Assuming NoScript's usage ratio is comparable to the average, approximately 5.4 million installations of FireFox are running NoScript. Let's ignore the fact that NoScript's usage ratio is probably much lower than the average, due to the fact that it breaks most web pages.
I'd wager that the average NoScript user has at least two machines, so the total number of NoScript users is probably less than 2.7 million.
There are over 230 million internet users in the USA.
Even if 100% of NoScript users were Americans, they form 1% or less of the general population. If you, like me, believe that I have been generous to NoScript here, it is likely that no script users are no more numerous than 1 in 1,000.
Even if the user is using NoScript, they can whitelist your site. You can probably add <noscript>WARNING: THIS SITE IS BUSTED WITHOUT JS</noscript> to the top of your page and call it a day. If you are feeling generous, redirect no-script users to the mobile version of your site and tell them why.
tldr: Assume that human user agents have Javascript.
