Stray dogs?

I saw a dog wandering around Chicago today around the north side. He had no collar, looked almost sickly, was not neutered, and had several growths on him. Because of his alarming appearance and rather large size, I did not approach him directly. But being surrounded by busy streets, I was incredibly nervous he would get hit by a car. I called 311 (non-emergency services) and it took me almost 10 minutes to get through. By the time they answered, the dog was out of site and had crossed a street towards another direction. After describing his appearance and where he was headed, they said they'd send someone out and thanked me for the call.

What kind of priority do these calls have? Do they actually come out and search for the dog? If they don't see him, do they search around the area further? Where do they take him?

I know many people saw him and most likely tried to call as well. It makes me terribly sad to see him wandering about on his own.