This city is on the western shore of Lake Hamana. The Tokaido passed through this land, and at the lake’s outlet a checkpoint was placed that strictly inspected people and goods. A person born in this land invented a machine for weaving cloth, and later laid the foundation of a great group of automobile firms. Even now, automobile plants in the line of that current support this city’s livelihood. In the Heisei era, this town that held the checkpoint widened its city area by joining the checkpoint town, and now keeps its population somewhere near sixty thousand. Kosai’s numbers are the record of a city inscribed with the history of the Tokaido checkpoint and the loom.
A city at the westernmost edge of Shizuoka Prefecture, reaching from the western shore of Lake Hamana to the prefectural border with Aichi. Because this city incorporated the Tokaido checkpoint town in 2010, the step in the population on the city area appears between 2005 and 2010, when the merger is mirrored in the census. The population on the former city alone was 44,057 in 2005; on the merged city area it was 60,107 in 2010, and it has since kept somewhere near sixty thousand, to 57,885 in 2020. What I (Atlas) want to read here is not the sign "a city at the prefecture’s western edge," but the causal thread: how the history of the Tokaido checkpoint and the loom is translated into today’s population and finances.
01 · See the present Kosai in its numbers
In the latest Population Census the population is about 58,000 (57,885 in 2020). Because this city incorporated the Tokaido checkpoint town in 2010, the step in the population on the city area appears between 2005 and 2010, when the merger is mirrored in the census. The population on the former city alone was 44,057 in 2005; on the merged city area it was 60,107 in 2010, 59,789 in 2015 and 57,885 in 2020, keeping somewhere near sixty thousand.
Looking inside the figures, the form of an industrial city west of Lake Hamana appears. The share aged 65 and over rose by about thirteen points in twenty years, from 15.1% on the former city alone in 2000 to 27.8% on the merged city area in 2020, but still has not reached three in ten. The household-with-children share is 22.0% in 2020, and the Childcare Waitlist was zero in both 2024 and 2025. The Fiscal Capacity Index was 1.00 in fiscal 2023 — a high level that can cover expenditure with its own tax revenue alone, without relying on the local allocation tax. The figure of a city holding the Tokaido checkpoint, keeping its population near sixty thousand while holding automobile plants, appears in the numbers. Why it takes this shape cannot be read without going back over the history of the lake, the checkpoint and the loom.
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 western shore of Lake Hamana, the Tokaido checkpoint, the inventor of the loom, the automobile plants, the incorporation of the checkpoint town — the history behind the numbers
This city’s skeleton is set by the landform of the western shore of Lake Hamana, by the Tokaido checkpoint placed at the lake’s outlet, by the person born in this land who invented the loom, by the automobile plants strung from there, and by the incorporation of the checkpoint town. The starting layer is the lake and the checkpoint. This land is on the western shore of Lake Hamana, and the Tokaido passed through here. At the lake’s outlet was placed a checkpoint that strictly inspected people and goods, and nearby two Tokaido stations flourished. The checkpoint at the lake’s outlet was this land’s old center.
In this land that held the checkpoint, a modern loom was born. A person born in this land invented a machine for weaving cloth, and later laid the foundation of a great group of automobile firms. In the line of that current, automobile plants located here, and the value of manufacturing shipments became among the highest in the prefecture. The path to becoming a city, too, mirrors this city. It gained city status in the 1970s, and in 2010 it incorporated the checkpoint town at the lake’s outlet. The western shore of Lake Hamana, the Tokaido checkpoint, the person who invented the loom, the automobile plants, and the incorporation of the checkpoint town — this city’s shape stands upon the history of the checkpoint and the loom held by the western shore of Lake Hamana.
Source: Kosai City / Arai Checkpoint (the "Imagiri Checkpoint" of the Tokaido placed at Arai on the western shore of Lake Hamana; Arai-juku / Shirasuka-juku flourished as Tokaido post towns — overview) / Kosai City / Sakichi Toyoda (Sakichi Toyoda, who invented the automatic loom and laid the foundation of the Toyota Group, was from the Washizu district [former Yamaguchi Village]; the Sakichi Toyoda Memorial Hall is here — overview) / Kosai City (city status in 1972; the incorporation of Arai Town on 2010-03-23; the westernmost city of Shizuoka, reaching from the western shore of Lake Hamana to the prefectural border with Toyohashi, Aichi; an automotive-related city holding Suzuki’s Kosai plant — overview)
03 · West of Lake Hamana, keeping the population while holding automobile plants
What characterizes Kosai is that, while holding the history of the Tokaido checkpoint and the loom, it keeps its population near sixty thousand while holding automobile plants. The 44,057 of the former city alone in 2005 became 60,107 on the city area that incorporated the checkpoint town in 2010, and has since kept near sixty thousand, to 57,885 in 2020. Behind the fact that, while many provincial cities lose population, this city has held its population, can be read this: automobile plants strung from the person who invented the loom located here, and held workplaces.
On the other hand, the share aged 65 and over, at 27.8% in 2020, still has not reached three in ten, even while rising by about thirteen points in twenty years. The Childcare Waitlist was zero in both 2024 and 2025, and the household-with-children share is 22.0% in 2020. The Fiscal Capacity Index of 1.00 is a level that can cover expenditure with its own tax revenue alone, high enough not to rely on the local allocation tax. It can be read that the manufacturing livelihood, holding automobile plants, supports the tax source high. The city holding the Tokaido checkpoint still keeps its population near sixty thousand while holding automobile plants, raising the city’s age. The population is roughly level, the aging is just short of three in ten, and the fiscal stamina is high enough to cover expenditure with its tax revenue alone. This height of covering expenditure on its own is the consequence of the automobile plants, grown from the land of the checkpoint, thickening the tax source.
Source: Population Census (Statistics Bureau, MIC) / Local Government Finance Survey, Fiscal Capacity Index (MIC) / Childcare Facility Status Report (Children and Families Agency)
04 · The western shore of Lake Hamana that held the Tokaido checkpoint and the automobile plants
Kosai holds several functions of its own. One is the history of being the land that held the Tokaido checkpoint, where the Tokaido passed along the western shore of Lake Hamana and a checkpoint that strictly inspected people and goods was placed at the lake’s outlet. Another is its character that a person born in this land invented a machine for weaving cloth, and the automobile plants strung from there located here, so that the value of manufacturing shipments became among the highest in the prefecture. And the landform — the western shore of Lake Hamana reaching to the prefectural border with Aichi — drew both the checkpoint and the automobile plants into this city.
Kosai is a city where the western shore of Lake Hamana held the Tokaido checkpoint and the automobile plants. From the checkpoint at the lake’s outlet, to the inventor of the loom, the automobile plants, and the incorporation of the checkpoint town — the geography of "the western shore of Lake Hamana reaching to the Aichi border" set down the Tokaido checkpoint, and later drew automobile plants onto that same shore. From the checkpoint town that strictly inspected people and goods at the lake’s outlet came the person who invented a machine for weaving cloth. That invention strung onward, and now a group of automobile plants whose shipment value is among the highest in the prefecture stands on the same shore.
Source: Kosai City / Arai Checkpoint (the "Imagiri Checkpoint" of the Tokaido placed at Arai on the western shore of Lake Hamana; Arai-juku / Shirasuka-juku flourished as Tokaido post towns — overview) / Kosai City / Sakichi Toyoda (Sakichi Toyoda, who invented the automatic loom and laid the foundation of the Toyota Group, was from the Washizu district [former Yamaguchi Village]; the Sakichi Toyoda Memorial Hall is here — overview) / Kosai City (city status in 1972; the incorporation of Arai Town on 2010-03-23; the westernmost city of Shizuoka, reaching from the western shore of Lake Hamana to the prefectural border with Toyohashi, Aichi; an automotive-related city holding Suzuki’s Kosai plant — overview)
05 · Atlas note — from the checkpoint to the loom, from the loom to the plant
Lay out Kosai’s numbers and the indicators of an industrial city west of Lake Hamana line up: a population kept near sixty thousand, an aging rate of 27.8%, a household-with-children share of 22.0%, and a fiscal capacity of 1.00. But when I (Atlas) read this city with the accountant’s eye, what I want to read is the chain of history — that this city "gave rise to the inventor of the loom in a land that held the Tokaido checkpoint." The Tokaido passed along the western shore of Lake Hamana, and a checkpoint was placed at the lake’s outlet. A person born in that land invented a machine for weaving cloth, and later laid the foundation of a great group of automobile firms. The chain — that the land holding the checkpoint gave rise to the loom and called the automobile plants — explains well the Fiscal Capacity Index of 1.00, a height that needs no reliance on the local allocation tax.
One more thing to weigh is that this city "still holds its aging short of three in ten." Amid the many provincial cities whose aging rate advances past three in ten, this city is still at 27.8% in 2020, not reaching three in ten. One can also read that the automobile plants hold workplaces and have held back the young generation to a degree. The overlap — that the city holding the Tokaido checkpoint keeps its population near sixty thousand while holding automobile plants, holds its aging short of three in ten, and places its fiscal capacity at a height that covers expenditure with its tax revenue alone — is peculiar to this city. From the land of the checkpoint that strictly inspected people and goods at the lake’s outlet came the person who invented a machine for weaving cloth, and that invention strung onward until now a group of automobile plants whose shipment value is among the highest in the prefecture stands on the same shore. This chain, joined in a single thread — checkpoint, loom, plant — bears both the fiscal capacity of 1.00, a height needing no allocation tax, and the aging held short of three in ten. A single geography has called three generations of industry in turn. I (Atlas) leave the matter at noting that thread beside the numbers.
Source: Population Census (Statistics Bureau, MIC) / Kosai City / Arai Checkpoint (the "Imagiri Checkpoint" of the Tokaido placed at Arai on the western shore of Lake Hamana; Arai-juku / Shirasuka-juku flourished as Tokaido post towns — overview) / Kosai City / Sakichi Toyoda (Sakichi Toyoda, who invented the automatic loom and laid the foundation of the Toyota Group, was from the Washizu district [former Yamaguchi Village]; the Sakichi Toyoda Memorial Hall is here — overview) / Kosai City (city status in 1972; the incorporation of Arai Town on 2010-03-23; the westernmost city of Shizuoka, reaching from the western shore of Lake Hamana to the prefectural border with Toyohashi, Aichi; an automotive-related city holding Suzuki’s Kosai plant — 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 (Daiki 2026-06-02)) handled the shaping of the text. Evaluative or predictive language (such as “a good buy” or “attractive”) is intentionally left out. Revision id: wave24_1