The island which has existed longest is apparently Madagascar, which separated from Africa perhaps 85 million years ago. There were proposals to name it Lomu Island, after a rugby player of Tongan ancestry. However, it was thought that the island may be merely the latest incarnation of an island which has appeared near that site several times before, most recently as Lateiki Island, which existed from 1976 to 1978. The new island might exist for only a few years before eroding or subsiding beneath the waves. While this count may essentially be accurate, Canada probably has far more islands than Finland, as it has immense areas of island-strewn lakes and thousands of miles of rocky coastline.
Several countries appear to have no islands at all.
In fact, there are 27. The Thirty Thousand Islands of Georgian Bay, Ontario, probably do include several thousand islands. The Thousand Islands on New York and Ontario number about 1,500. Islands in a Lake Lake of the Woods, shared by Ontario, Minnesota, and Manitoba, is said to contain 14,000 islands. The most populous island country is Indonesia, which has about 200 million inhabitants.