I can answer the first one because I lived very close to it. Yes, there is a Palos Hills near Chicago, it is a suburb on the southwest side. There is no "Palos Hills High School" as far as I know though, the only high school in Palos Hills is Stagg. Which makes sense since I doubt the show could use a real high school's name.
Palos Hills Map
I can answer the second as well, because Google exists. There is a San Pedro in the Los Angeles area of California. In fact it looks to be within the city of Los Angeles itself. I certainly do not know of any San Pedro around Palos Hills / Chicago, and I know most of the cities around here. In fact "San" as part of a city name is not a Chicago thing at all, it's a California thing based on Spanish ministries, so it is safe to say that they are not referring to anything in the Chicago area with this one.
San Pedro Map