Last year probably around -10 F, don't remember. Today was -6 F when I left the house.
I went to grad school in South Bend, and remember one winter, maybe it was 1989-90, when it got into the -20's.
Under the coldest conditions, I wear my cold weather ski gear, including ski helmet and goggles, and then some insulated boots. I probably look pretty comical, but it gets me to my destination.