Is Japan's Population Concentrated on Hokkaido and Shikoku?

No. The vast majority of Japan's population (~125M) lives on Honshu, the largest main island.

Population Distribution (approx.)

• Honshu: ~80% (includes Greater Tokyo ~37M, Keihanshin ~19M, Nagoya ~9M).
• Kyushu: ~10% (Fukuoka, Kitakyushu, Nagasaki).
• Hokkaido: ~4.5% (Sapporo ~1.9M).
• Shikoku: ~3% (Matsuyama, Takamatsu, Kochi, Tokushima).

Hokkaido and Shikoku are sparsely populated by comparison—mountainous, rural, with aging demographics. The "Taiheiyo Belt" (Pacific Belt) on Honshu is the continuous urban corridor driving Japan's economy.