Curious, I Googled a bit, but can't find a definitive source. It is true that most politicians are local. Here is an infographic that shows 96% are local:
I don't have a written source, but I think it's safe to say that the majority of elected offices in the United States are local/municipal, and many (most?) of those are unpaid. And if they're not unpaid, they usually only pay a few thousand a year, if that.
