American would not have been in Illinois: the brand for Illinois and Wisconsin (and several other states) was Standard, although after a certain point, the company sold "Amoco fuels."

Thanks for the tip, carpwoman! Looking at Lemont from the satellite view makes me think that's a good possibility given the similar terrain. My Uncle lived about 50 miles East of Lemont in Valparaiso, Indiana and took trips across the country.

I don't know why, but my first thought is Lemont, Illinois.