We've got two main organizations locally, the Inland Northwest Freethought Society (affiliated now with the national Freedom from Religion Foundation) and the Spokane Secular Society.
The term does naturally presuppose some manner of godly faith (rather than, say, a naturalistic "faith" that the rules of nature operate regularly throughout the universe).
It is not an uncommon perspective to be heard for atheists and agnostics, which is the reason why local secular organizations have been formed over the years, as a support group and place of refuge as well as lighter socializing and connection to a broader world of thought.
How do we "know" all that dark matter and dark energy exist at all? Well, it's precisely because astrophysicists know so much about how the regular matter operates.