I lived in the Bible Belt and didn't know anyone who believed as I did, so I founded a freethinker group (on MeetUp) that has over 1000 members on FB and probably about 50 people who are active members. I made several good friends that way!

This is a great question deserving great answer for those in need. I became atheist alone as I grew up. I could hang out with christians, hell, I lived with a christian scientist that was second reader in her church and we still best friends and spent time together and do friend dates. But if you need more atheist in your life they will appear, there are many in the closet as well as many open.

That is a tough one. I've been agnostic for many year, and after being use to the church community I find I still haven't filled that void. I am looking into joining an astronomy club, both to learn, but also looking for community.

Amidst thoughts found in books written mostly by people long dead.

I have not tried it yet, but several people have mentioned to me that you can find a lot of agnostics and atheists at a Universalist Church, and they've enjoyed that community.

Look for meet-up groups based on other interests, like politics, sports, or hobbies.

Well until I found this site I was pretty much on my own.

Here's good.

This site.