Kasaoka-shi

In the 2020 Population Census the population of Kasaoka-shi is 46,088 — about 46,000. Its trend is a single road of decline: from 59,300 in 2000 to 57,272 in 2005, 54,225 in 2010, 50,568 in 2015, and 46,088 in 2020 — a loss of more than thirteen thousand over twenty years. A population once near sixty thousand fell below fifty thousand.

Looking inside the figures, the shape of a Seto Inland Sea port town deepening in age appears. The share aged 65 and over rose from 25.8% in 2000 to 37.0% in 2020, nearing four in ten. Households with children make up a low 16.6% (2020), and the Childcare Waitlist was zero in both 2024 and 2025. The Fiscal Capacity Index was 0.56 in fiscal 2023 — a mid-level for a small or mid-sized city, covering half and a little more of expenditure with its own tax revenue. The numbers show the island-and-reclamation port town losing population and deepening in age while finances hold at a middle level. Why it takes this shape cannot be read without tracing the history of the islands and the reclamation.

What set down the town of Kasaoka is the geography of islands floating in the Seto Inland Sea and the bay that held them. The old layer is the port and the islands. Kasaoka opened as a port town as far back as the Kamakura era, and the foundations of the port are said to have been laid under a clan that governed this land. Off the city spread the Kasaoka Islands, some thirty large and small, of which eight are inhabited. Many of these islands are made of granite, and one in particular was known as a source of fine stone. The granite of the Seto Inland Sea islands and the craft of cutting stone long supported building across the country. Islands floating in the sea, and the port that holds them, make up this town’s deep layer.

And in the modern era this town set about works that greatly changed the bay itself. The reclamation of Kasaoka Bay, begun in 1966, was completed fully in 1990, taking some twenty-two years and a great sum. The former bay became land and changed into farmland and the like. By this reclamation the bay’s scenery was greatly repainted, and the breeding ground of an old creature that had once bred in this bay was moved to another channel. A port town holding the Seto Inland Sea islands passed through a great undertaking that turned bay into land. Onto the old history of sea and islands, the modern work that rewrote the bay was laid, and the present landform of Kasaoka was made.

What characterizes Kasaoka-shi is that, while carrying the history of a port town holding islands, it is losing population and deepening in age. From 59,300 in 2000 to 46,088 in 2020, it lost more than thirteen thousand over twenty years. Even in the mainland town center the flow of the younger generation moving to the cities continues, and one can read that on the offshore islands in particular, population loss and aging have advanced deeply. Island life, cut off by the sea, tends to carry more inconvenience than the mainland, and the flow of the younger generation leaving the islands has continued. That the share aged 65 and over neared four in ten at 37.0% in 2020 is the sign of that population structure.

Meanwhile fiscal strength holds at a middle level. A Fiscal Capacity Index of 0.56 is a level that covers half and a little more of expenditure with its own tax revenue, mid-range for a small or mid-sized city. One can read that the farmland born of reclamation and the mainland’s places of business give a certain thickness to the tax source. The Childcare Waitlist, too, was zero in both 2024 and 2025. The population falls, aging nears four in ten, and still fiscal strength stays at a middle level. A port town holding in one body lands of differing nature — islands, mainland, and reclaimed ground — walks several opposing currents at once; that shape shows in the numbers. The single line for the whole city is no more than the value of adding the mainland town center and the offshore islands — two things that fall differently — and dividing by two.

In Kasaoka, several functions rooted in the geography of the Seto Inland Sea are inscribed. One is the history of a port going back to the Kamakura era and the Kasaoka Islands, some thirty large and small — a deep layer holding islands that float in the Seto Inland Sea. Another is its character as a source of the fine stone cut from a granite island, keeping the craft of cutting Seto Inland Sea stone. And the reclamation of Kasaoka Bay, which took twenty-two years from 1966, gives this town the distinctive structure of works that turned bay into land.

Holding more than thirty islands in the Seto Inland Sea and a shallow bay — that geography called forth a life of port and islands and, in the modern era, drew in the reclamation that turned bay into land. From port and islands, to an island that cuts stone, and on to a town that turned bay into land, functions piled up in layers. At the western-edge Seto Inland Sea position of the prefecture, onto the history of a port town holding islands, the memory of the reclamation that turned bay into land folds over. The town of Kasaoka rides on those two.