| Koshimizu | |
| Native Name Lang: | ja |
| Settlement Type: | Town |
| Seal Type: | Emblem |
| Pushpin Map: | Japan |
| Pushpin Map Caption: | Location in Japan |
| Coordinates: | 43.85°N 172°W |
| Subdivision Type: | Country |
| Subdivision Name: | Japan |
| Subdivision Type1: | Region |
| Subdivision Name1: | Hokkaido |
| Subdivision Type2: | Prefecture |
| Subdivision Name2: | Hokkaido (Okhotsk Subprefecture) |
| Subdivision Type3: | District |
| Subdivision Name3: | Shari |
| Extinct Title: | Now part of |
| Leader Title: | Mayor |
| Leader Title1: | Vice Mayor |
| Unit Pref: | Metric |
| Area Total Km2: | 287.04 |
| Population Total: | 5,029 |
| Population As Of: | May 1, 2017 |
| Population Density Km2: | auto |
| Timezone1: | JST |
| Utc Offset1: | +09:00 |
| Blank Name Sec1: | City hall address |
| Blank Name Sec2: | Climate |
| Blank Info Sec2: | Dfb |
is a town in Okhotsk Subprefecture, Hokkaido, Japan.
As of May 1, 2017, the town had an estimated population of 5,029 and a population density of 18 persons per squared kilometre.[1] The total area is 287.04 km2.
Koshimizu's mascots are and . They are appointed as mascots on October 3, 2013.[2]