Let’s see… the main islands of Japan are (in alphabetical order): Hokkaido, Honshu, Kyushu, and Shikoku.
Honshu is the big one, and is known as the mainland of Japan.
As for the rest… well… Japan is actually an archipelago known as Nihon Rettō (日本列島).
For the purpose of Japan’s official count of ‘island’s’ in the archipelago, an island is considered to be land greater than 100 meters in circumference, which means it is smaller than my front yard.
Of these 6,852 pockets of land, a total of 430 are inhabited… and I assume that means by humans… but I saw that fact in Wikipedia, so who the heck knows? It wasn't specific.
If you wish to know all the islands of the Japanese archipelago, feel free to click HERE.
I only visited two of the islands during my three years-plus in Japan, but even then, I couldn't see everything.
Yeah - Kyushu and Honshu.