In Your Basement
If your house has a basement, then it's probably been home to some ants at some point. Subterranean, unfinished basements and cellars are particularly susceptible, but even if you have a finished daylight basement, it's still closer to the earth than the upstairs so it's going to be more prone to ant action. If you have ants in the basement, they're doing the same thing they're doing in your kitchen -- foraging for food. Unless you keep food in your basement, the ants will be stuck with whatever living or dead insects they can find. It's tough to keep ants out of your basement, but keeping it clean will help.