How do you shut down an ice maker for the winter?

If there is a basement, locate the pipe where it goes through the exterior wall leading to the outside water faucet. This is your starting point.

Follow the pipe under the flooring, going towards the direction of where the water comes into the house from the meter. The first valve from your starting point is the shutoff valve for that faucet.

Do the same for each and every other outside faucet.

If there is no basement, you will have to access the shutoff valves by going into the crawl space. (I would take bug spray with me because of the Spiders and their webs!)