Behind this town rises a limestone mountain that shows its white skin. It is a mountain of limestone where ancient coral and shells piled on the sea floor and were upheaved by the movement of the crust. With this limestone as material, the town became a land that makes cement. The limestone dug in the mountain is carried by belt conveyor to the seaside factory, and the products are sent out by ship. The intricate bay spreading before the town deepens abruptly from near the shore, and takes in large vessels. This land of the limestone mountain and the ria bay did not join the Heisei mergers, and while walking an independent path, has greatly lost population. Tsukumi’s numbers are the record of a town in which the cement town and the independent path are inscribed.
A city that opens on the ria coast, in the southeast of Oita Prefecture. The population has greatly fallen, from 23,164 in 2000 to 16,100 in 2020. Because this city did not pass through a Heisei merger and has walked independently, there is no merger-derived step in its recent population transition. What I (Atlas) want to read here is not the sign "a city of the southeast of the prefecture," but the causal thread: how the past of the cement town and the independent path is translated into today’s population and finances.
01 · Seeing the present Tsukumi in its numbers
In the latest Population Census the population is about 16,000 (16,100 in 2020). Because this city did not pass through a Heisei merger and has walked independently, there is no merger-derived step in its recent population transition. From the 23,164 of 2000, to the 21,456 of 2005, the 19,917 of 2010, the 17,969 of 2015, and the 16,100 of 2020, some seven thousand were lost over twenty years.
Looking inside, the figure of a cement town greatly raising its age appears. The share aged 65 and over rose from 39.7% in 2015 to 45.0% in 2020, passing four in ten by a wide margin. The household-with-children share is 14.0% in 2020, and the crude birth rate is 3.6 per thousand in 2020. The Childcare Waitlist was zero in both 2024 and 2025. The Fiscal Capacity Index was 0.39 in fiscal 2023 — a level able to cover only a little under four-tenths of expenditure with its own tax revenue, with a large degree of reliance on the local allocation tax. The figure of a land of the limestone mountain and the ria bay, greatly losing population while remaining independent without a merger and deepening its aging, shows in the numbers. Why it takes this form cannot be read without going back to the past of the limestone mountain, the cement town and the ria bay.
Source: Population Census (Statistics Bureau, MIC) / Local Government Finance Survey, Fiscal Capacity Index (MIC) / Childcare Facility Status Report (Children and Families Agency) / Real Estate Information Library (MLIT)
02 · The limestone mountain, the cement town, the deep ria bay, the independent path — the history behind the numbers
This town’s skeleton is set by the landform of a limestone mountain, the cement town, the deep ria bay, and the independent path. The starting layer is the limestone mountain. Behind this town rises a mountain of limestone where ancient coral and shells piled on the sea floor and were upheaved by the movement of the crust. This landform — where not the bottom of the earth but the mountain itself is the resource — was the foundation of this town.
This limestone mountain gave rise to the cement town. From the Taisho era on, factories making cement with limestone as material were built one after another, and the town walked as a cement town. The limestone dug in the mountain was carried by belt conveyor to the seaside factory, and the products were sent out by ship. The intricate bay spreading before the town deepens abruptly from near the shore, and takes in large vessels. The path to becoming a city, too, mirrors this town. This town attained city status in the mid-Showa era, but did not join the Heisei mergers, and has walked independently. The limestone mountain, the cement town, the deep ria bay, and the independent path — this town’s form stands upon the past of the cement town that the limestone land, where the mountain itself is the resource, carved.
Source: Tsukumi City / limestone and cement (holding mountains of limestone formed by the upheaval of ancient coral reefs and the like; cement production began in the Taisho era and developed as the core industry; carried by belt conveyor from the quarry to the bayside factory — overview) / Tsukumi City / the ria bay (a ria coast where the shore deepens abruptly, allowing large vessels to enter port; one reason the limestone industry developed here — overview) / Tsukumi City (Tsukumi Town attained city status in 1951; the ria coast in the southeast of Oita Prefecture; did not take part in the Heisei mergers and continued independently — overview)
03 · In a land of the limestone mountain and the ria bay, greatly losing population while remaining independent
What characterizes Tsukumi is that, while it holds the past of a cement town, it is greatly losing population independently, without passing through a merger. From the 23,164 of 2000 to the 16,100 of 2020, some seven thousand were lost over twenty years. Even in this land that has walked as a cement town, one can read that much of the younger generation moved toward the larger cities, and the town’s age as a whole greatly rose. That the share aged 65 and over passed four in ten by a wide margin at 45.0% in 2020, and that the crude birth rate is low at 3.6 per thousand in 2020, are expressions of that.
On the other hand, the Childcare Waitlist was zero in both 2024 and 2025, and the household-with-children share is 14.0% in 2020. The Fiscal Capacity Index of 0.39 is a level able to cover only a little under four-tenths of expenditure with its own tax revenue. The land of the limestone mountain and the ria bay now, while remaining independent without a merger, deepens its aging while greatly losing population. The location where the mountain itself is the resource once drew in the cement factories and the workforce. That same single-leg structure now, together with the automation of the industry and the aging of those who bear it, calls forth a thinning of a crude birth rate of 3.6 and an aging rate of 45.0%. The mountain fattened the town, and now the same mountain mirrors the town’s thinning.
Source: Population Census (Statistics Bureau, MIC) / Local Government Finance Survey, Fiscal Capacity Index (MIC) / Childcare Facility Status Report (Children and Families Agency)
04 · A limestone land where the mountain itself is the resource held a deep ria bay, this past
The functions Tsukumi holds are not one. A mountain of limestone where ancient coral and shells were upheaved rises behind, and the mountain itself is the resource. With that limestone as material it has made cement, carrying it from the mountain to the seaside factory by belt conveyor. And the intricate bay deepens abruptly from near the shore, and takes in large vessels.
From the landform of a limestone mountain, to the cement town, the deep ria bay, and the independent path — the geography of "a limestone mountain where ancient coral was upheaved, and a ria bay that deepens abruptly" gave rise to the cement town and held a bay that takes in large vessels. The two landforms of the limestone mountain and the ria bay are folded together in the same single place of the southeast of Oita Prefecture, and set the present form of Tsukumi.
Source: Tsukumi City / limestone and cement (holding mountains of limestone formed by the upheaval of ancient coral reefs and the like; cement production began in the Taisho era and developed as the core industry; carried by belt conveyor from the quarry to the bayside factory — overview) / Tsukumi City / the ria bay (a ria coast where the shore deepens abruptly, allowing large vessels to enter port; one reason the limestone industry developed here — overview) / Tsukumi City (Tsukumi Town attained city status in 1951; the ria coast in the southeast of Oita Prefecture; did not take part in the Heisei mergers and continued independently — overview)
05 · Atlas’s note — in a land of the limestone mountain and the ria bay, one industry tells of both flourishing and thinning
Lay out Tsukumi’s numbers and the indicators of a cement town deepening its age line up: a population greatly falling while remaining independent, an aging rate of 45.0%, a household-with-children share of 14.0%, a crude birth rate of 3.6, and a fiscal capacity of 0.39. What I want to read here is that this town "has had both of two landforms — the limestone mountain behind and the deep ria bay before — support the cement town." Limestone is dug from the mountain, and the bay’s depth takes in large vessels. That the mountain of material and the deep bay that carries the products are together in the same single town rooted the cement town in this land. The chain by which the supply ground of material and the outlet of products being contiguous decided the location of the industry explains this town’s past well.
Another thing I want to consider is that this town holds numbers showing the deepening of age — an aging rate of 45.0% and a crude birth rate of 3.6. Even in this land that has walked as a cement town, the outflow of the younger generation and the falling birth rate overlapped, and the town’s age greatly rose. A small city supported by one industry greatly loses population, together with the automation of that industry and the aging of those who bear it.
Seen with the eye of accounting, that the supply ground of the industry — the limestone mountain — and the outlet — the deep ria bay — were contiguous is the very thing that tells, at once, of this town’s flourishing and its thinning. Whether to view it as a land where the mountain itself is the resource, or as a small city that has entrusted its fortune to one industry, changes with what one turns one’s eyes to. That the supply ground of limestone, where the mountain itself is the resource, and the outlet of the deep ria bay were contiguous is the very thing that tells, at once, of this town’s flourishing and its thinning.
Source: Population Census (Statistics Bureau, MIC) / Tsukumi City / limestone and cement (holding mountains of limestone formed by the upheaval of ancient coral reefs and the like; cement production began in the Taisho era and developed as the core industry; carried by belt conveyor from the quarry to the bayside factory — overview) / Tsukumi City / the ria bay (a ria coast where the shore deepens abruptly, allowing large vessels to enter port; one reason the limestone industry developed here — overview) / Tsukumi City (Tsukumi Town attained city status in 1951; the ria coast in the southeast of Oita Prefecture; did not take part in the Heisei mergers and continued independently — overview)
Editor’s note: all figures and sources are drawn from official statistics. The prose follows Atlas’s voice, and AI (atlas-handcrafted-reverse-v1 (wave34-west 2026-06-04)) handled the shaping of the text. Evaluative or predictive language (such as “a good buy” or “attractive”) is intentionally left out. Revision id: wave34w_