One website has my town (70,000. pop) with 318 active notaries. A friend of mine lives two counties away, but up in the foothills and has four notaries.
What is average? I cannot imagine what 318 notaries would be doing or where they would be doing it.
Keep in mind that many (perhaps most) notaries are not mobile notaries. There are notaries in banks, law offices, universities, and so on. In my state, Vermont, every police officer has the powers of a notary.
I know the courts have been making it easier to file court papers in recent years, but in the past many of the things cops submitted to courts to get arrest warrants or search warrants had to be sworn to. If all the cops are notaries, it’s easy to find someone to administer an oath, either to another cop, or to a witness.