Lake County
My old home county. Large parts of this county are urban. LARGE parts. However, there are several very nice preserves here that are worth a visit, some of them in the heart of the urban areas. Give it a chance! My own personal goal is to canoe the Little Calumet, which may be the most polluted stream in the state, but it looks fascinating. The Deep River is mentioned in the Indiana Canoeing Guide, and is similar to the Little Calumet, but I've never heard of anybody canoeing either one. Any field reports out there?
Cressmoor Prairie Nature Preserve
Hoosier Prairie Nature Preserve
Indiana Dunes National Lakeshore