I feel foolish bothering folks with this question but I am puzzled and concerned.

I live in a modest, tree-canopied suburban neighborhood in DuPage county. For the past week or so, I have casually noticed that there has not been a single squirrel in the neighborhood. Usually, there is a generous squirrel population running about. Is this normal?

It is normal for wildlife populations to fluctuate. Unless you are finding large numbers of dead squirrels, there should be nothing to be concerned about. I'm sure that you'll start seeing more squirrels soon. They are in their second breeding season.

All of our squirrels are gone.....I've noticed this happened about 14 months ago...used to have several with their babies coming for peanuts every day....our dog was sick with lymph node cancer and this is a second dog that has come down with the same diagnosis....perhaps animals are being poisoned by grass weed killer, rose pests sprays, rat killer mixing with water running down the side of our hill....what are we doing with pesticides? We can't kill ants with ant spray that works but we use stuff strong enough to kill squirrels and dogs?