“Every, International Airport, in the United States is considered a border location.”
As well as a few in Canada. I flew through Canada once on Canadian, and went through entry via US Customs and Immigration authorities in Vancouver. I flew from Canada on Air Canada and went through entry in Toronto. It allows the onward flight to proceed to a domestic terminal.
I’ve heard some people remark that international airports in small cities are aggrandizing themselves by calling themselves “international”. “Podunk Corners International Airport”. “International” means that there are customs and immigration facilities there.
It also means commercial flight operations may be conducted 24 hours a day.