I have a bird that started coming to my house in Northern Ohio. In a city right near Lake Erie.Hmm, I certainly can't think of any other North American bird that seems like a sparrow that would have things on their head, looking like little ears, other than a Horned Lark.
The fact that you live near open hillside is a point in favor of Horned Larks which like open areas. The fact that it is roughly the size of a Fox Sparrow would also point to a Horned Lark. However, that you don't see the typical Horned Lark head patterning in black and yellow would seem to indicate otherwise.
I suppose it is possible that you've got a very dull plumaged female(s) or a group of immatures exhibiting the horns but not yet in fullcolor plumage???
Is it possible that the darker film you've placed on your windows is somehow filtering the colors/patterns more than you imagine it would?
A picture would definitely be worth a thousand words here...