Mice can get through a hole as thin as a pencil. Make sure that all tiny openings are sealed up. Mice can enter through the connections behind the dishwasher, stove, washer and dryer. They crawl up drain pipes under the sinks and
Where the water pipes and the wiring enter the house
Keep limbs from touching the roof, and check for tiny openings in crawl spaces too. Check all over the outside. Be sure there are no holes anywhere. Mice can squeeze through holes that you may assume are too high for them, a mouse can easily climb up a vertical surface. If you can fit your little finger in a whole then a mouse will have no problem getting in either.