Shizuoka静岡県
Kosai 湖西市
Data last updated:
Kosai, Shizuoka, Japan has a population of 55,167 (2025 national census). IPSS projections estimate 53,584 by 2030 and 42,841 by 2050 (a decrease of about 26.0% from 2020), with the share of residents aged 65+ rising from 27.9% in 2020 to 41.0%.Sources: Japan Census (Statistics Bureau), IPSS Regional Population Projections (2023)
2025
(Census)
55,167
2030
(Projection)
53,584
▼ -7.4%
2040
(Projection)
48,485
▼ -16.2%
2050
(Projection)
42,841
▼ -26.0%
Change vs. 2020 census
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Other municipalities in Shizuoka (静岡県)
Data Sources
- Portal Site of Official Statistics of Japan (e-Stat)（https://www.e-stat.go.jp/）
- National Institute of Population and Social Security Research (IPSS), Regional Population Projections (2023 ed.)
* This service uses the e-Stat API but its content is not guaranteed by the Japanese government.
Kosai Population Table (1980–2050)
Population by year: national census results (restated to current municipal boundaries) and IPSS (2023) projections based on the 2020 census.
| Year | Population | vs 2020 | Type |
|---|---|---|---|
| 1980 | 54,252 | ▼ -6.3% | Census |
| 1985 | 58,212 | ▲ +0.6% | Census |
| 1990 | 59,926 | ▲ +3.5% | Census |
| 1995 | 60,714 | ▲ +4.9% | Census |
| 2000 | 60,827 | ▲ +5.1% | Census |
| 2005 | 60,994 | ▲ +5.4% | Census |
| 2010 | 60,107 | ▲ +3.8% | Census |
| 2015 | 59,789 | ▲ +3.3% | Census |
| 2020 | 57,885 | — | Census |
| 2025 | 55,167 | ▼ -4.7% | Census |
| 2030 | 53,584 | ▼ -7.4% | Projection |
| 2035 | 51,104 | ▼ -11.7% | Projection |
| 2040 | 48,485 | ▼ -16.2% | Projection |
| 2045 | 45,708 | ▼ -21.0% | Projection |
| 2050 | 42,841 | ▼ -26.0% | Projection |
About Kosai
Overview
Kosai (湖西市) is a municipality in Shizuoka, Japan, with a population of 55,167 as of 2025.
Population Projection of Kosai
According to projections by Japan's National Institute of Population and Social Security Research (IPSS), Kosai's population is expected to reach 53,584 by 2030 (-7.4%), 48,485 by 2040 (-16.2%), and 42,841 by 2050 (-26.0%). A significant population decline is projected over the next three decades.
Aging Rate of Kosai
The aging rate (percentage of residents aged 65 and over) is 27.9% as of 2020 and is projected to rise to 41.0% by 2050. Over 40% of residents will be elderly, significantly affecting healthcare and social services needs.
National Comparison
Kosai's population decline rate exceeds the national average.
National and Prefectural Rank
- Population decline rate: Ranked #1174 out of 1903 municipalities nationwide.
- Aging rate in 2050: Ranked #1169 out of 1903 nationwide.
- Population size: Ranked #641 out of 1917 nationwide.
- Related: National rankings / All municipalities in Shizuoka
Earnings in Shizuoka (静岡県): Average salary in Shizuoka (静岡県) by age, gender and company sizejpsalary / MHLW Basic Survey on Wage Structure