You're in good company -- most schools have PTOs. About 75% of schools have independent parent groups. (PTO is the most common acronym, but as you mention, there are many.) About 25% of schools have PTAs, affiliated with the National PTA. There are 83,000 k-8 schools in the U.S. (elementary and middle schools), so there are tens of thousands of PTOs.
If you haven't seen it already, you can find information comparing PTOs and PTAs on our PTO vs. PTA page. Good luck!
- Craig
Links in this post:
PTO vs. PTA page: https:/classic.ptotoday.com//pto-vs-pta