Call Adult Protective Services, this is divided by county, go to apropriate county, call them tomorrow morning. Write a follow up letter after you speak to them, addressed to whomever it is you get on the phone. I suggest this, because a piece of paper is a tangible thing and they will likely respond in a like manner. Telephone call is not enough.
Document everything you see, talk to ALL your neighbors and ask them to do likewise. Sit down this evening and put together a little summary, with dates as best as you can remember them, include this in your letter to APS. You can contact the family also, and that may or may not be helpful.
Ron, we don't see eye to eye on much, but please don't F' around with this at all. You may find in speaking to folks in the neighborhood that you are not the only person who is concerned, Actually, I am fairly confident this will be the case.
Good luck man, stay cool, folks with dementia do poorly with confrontation.
Adult Protective Services (APS) Co Information
Looks like you could call them tonight, but I would wait until tomorrow morning