History Book Style Question

I would go with bibliography in the back, at a minimum. If the history is good and useful, especially if it's for a smaller place that's not going to get a lot of history books, it's nice to make it easier for future researchers.
And, it gives confidence to skeptical readers that you actually know something about the subject.

General attributions at random places in the text are a pain in the neck if you don't remember exactly where you read it.

How about both? Use the Bill Smith in-line example you gave (those are easier on the eyes and are more conversational), then provide a list of "Further Reading" at the end that gives more details about the sources?

Most commercial nonfiction (not academic—I can't speak to that) is written using the Chicago Manual of Style. I'd use Chicago if you want it to be professional. Newspapers and most magazines and online publications use AP Style. And most periodicals/dailies also have in-house style sheets.

Good luck with your project. I love the act of preserving local history.

My uncle worked for UPI and I had a number of friends who reported for them back in the day. So you're not alone, Jeff. I do miss it. One of their sports reporters was both a good friend and the source of many outrageous stunts in his effort to get the story. He was a colorful character.

Those were great old days.

As for your book, whatever you do, I will bet it's going to be exceptional. (And with the decline of local newspapers, there's a real need to preserve community history.)

I would suggest initial writing it with in-text citations, such as superscripts. In the later stages, you can remove them but will have a record of sources for each statement in case that is needed. In most cases in pop nonfic you don't say in text what the source of a fact is, you just say the thing and have the source in the bibliography.

I wonder if the strict citations could be preserved on your website as extra materials? Although I don't like them being separate from the text (for posterity), with books that do have value as sources it's amazingly frustrating to try to use them and then find out that they don't indicate exact source citations. Agree that for non-academics no citation method that preserves page numbers is going to look uncluttered on the page, but it also seems a shame if that work has been done not to have it accessible somehow. I once reviewed a book on cultural history and it was chock-full of great quotations that were new to me--all of which were kind of useless to use in other formats because there were no page citations (and reading dozens of books to get single-line quotes isn't really an option). You could also ask beta readers (or not, if you just wanted to see if they noticed citations) about formatting by giving a sample chapter and seeing how people respond.