When people live in or occupy a country, city, or town, they populate it. It doesn’t always refer to people — bugs might populate your kitchen if you leave half-eaten food out.
If your family lives alone on an island, you're the only people who populate it. You can also use this verb to mean "be present in," so you might say that vampires populate your favorite books, or that animated characters populate most of the movies you watch. Populate also means "fill in" in computing: "Will you populate that spreadsheet with data?" The Latin populus, or "people," is at the root of populate.