Just over the border in Indiana. I am not sure exactly what intersection was used but I bet I have been on this road. One of my favorite movies too.
Edit: Its Rt. 41 which I have been on a million times.
http://www.suburbanchicagonews.com/newssun/news/1881897,5_1_WA13_NWBYNW_S1-091113.articleLake Forester owns plane from Hitchcock thriller
November 13, 2009
By Linda Blaser Sun-Times Media
LAKE FOREST -- It's one of the most chilling chase scenes in film history: A suited Cary Grant runs for his life as a low-flying biplane buzzes, shoots and crop-dusts him before crashing into a fiery ball.
Bill Knauz of Lake Forest owns that biplane made famous in the 1959 Alfred Hitchcock thriller, "North by Northwest." A picture of Knauz' plane chasing Grant graces the cover of a 50th anniversary DVD/Blu-Ray edition of the award-winning film just released by Warner Brothers. snip
The appeal of owning the plane used in the film -- named by the American Film Institute as the seventh-greatest American mystery movie in history -- intrigued Knauz.
"It sat in a hangar in Bakersfield, California until I found it. The guy I bought it from actually restored it in Hawaii," Knauz said, explaining that surplus naval planes built before World War II were later converted to crop-dusters. The two-seater naval trainer became a one-seater with the front cockpit converted to hold crop-dusting chemicals. Crop-dusters put a beefed up engine on front to double the horsepower.
Here is the scene from the movie:
http://www.youtube.com/watch?v=A6gm5n5WmxY&feature=related