You will generally find willow trees growing along rivers. A single willow tree planted along a river drops twigs which are carried downstream and eventually they find a stopping place and a new tree grows form it. Over time their population increases substantially.

Of course you might find a place where humans planted a bunch of them, but I am not familiar with your area to tell you where that would be.

you can go to willobrook theres hundereds of them everywhere or willow springs a lil more south. In willow springs you can drive down archer ave through the forest preserve. Theres a river and lakes.