The American aerial county history series, Illinois

[Erato]

I just found an interesting resource for Illinois:  The American aerial county history series, Illinois.  This series of books was prepared in the 1950s.  Each volume covers a county and includes maps and a brief historical account. There are also numerous aerial photos of the towns and villages and of individual homes and farmsteads - I found a good shot of a family member's farm in Winnebago County.  I don't know how many counties were covered but some 30 or so are available online here:

http://www.gengateway.com/illinois/american_aerial_county_history_series.htm