Early last winter we had 3 mice get into the house - have no clue how as we've never had mice in this house. Two were quickly caught in traps, but the 3rd one wouldn't go near the traps & somehow survived. It finally found the poison & disappeared. Later, cleaning out the pantry (aka the furnace room), I found what it had been living on. I had stashed some bags of lentils to turn into chicken food, but forgot about them. The mouse found them & made quite a mess.

When we lived in the cabin (while working on the house) we never did figure out where the mice were coming in. So it was a habit to put everything that a mouse would like into jars. Adams peanut butter jars are very useful for this.

In the feed room I have 2 small dead refrigerators on their sides for chicken food. They are perfect for keeping the mice out. Even the mama bear who broke into the feed room wasn't able to do more than dump the feed. The fridges were still in good shape.