What is the absolute best area for training in the Chicago area and surroundings areas such as Lombard/Elmhurst etc…
Accessibility to hills and good routes?
Accessibility to a lake/pool?
Accessibility to off road and single track?
Dunno that there’s one perfect place. There is some good road riding in the Barrington area (up into Wisconsin) and I’ve done some decent rides out west in Batavia. And, obviously when you get into Wisconsin there is a ton of good road riding (Horribly Hilly Hundreds area, Madison IM course, etc.). And a fair number of people ride north of the city - Evanston, Glencoe, Highland Park - not the best rides, but good to get in 40-50 miles.
As for swimming, most people use Lake Michigan (Ohio Street beach) from June through September (after that it’s a mix of university pools, health club pools, wherever you can find nearby lanes available). Not really sure where the suburbanites swim (health club pools?).
Feel free to PM me if you want more details or have other questions.