Spider Identification Illinois
This is very likely an araneid (or Orb-weaver spider) in the family Araneidae. 

Without further evidence, it's hard to narrow down to a species. 

One possibility: 

Neoscona crucifera (Hentz orbweaver, spotted orbweaver or barn spider)



 Source: Will Cook 2001 

 

 Source: Wikipedia 


Description: 


Relatively variable in color (and sometimes pattern), but is usually rusty-red or golden orange color. 


This site suggests females are reddish-brown to brown and males are lighter brown with the sides of the carapace nearly black. 

Dorsal abdomen is brown and hairy; abdomen underside = black, with two white spots
The epithet crucifera refers to the cross-like pattern on their back
Legs have alternating light and dark brown bands. 

Size: females = 9.5-19 mm long; males = somewhat smaller
Web: very large (up to 0.61 m diameter) and often on buildings and other man-made structures
Range: Eastern/Central USA + Mexico  


According to Will Cook, 


  Several other species of Neoscona are confusingly similar...Other species usually have a bolder pattern.


We can rule out Neoscona domiciliorum because Illinois is west of its range and the colroation is different. [Source].