| Nishiōizumimachi | |
| Native Name: | 西大泉町 |
| Native Name Lang: | ja |
| Settlement Type: | Enclave district |
| Subdivision Type: | Country |
| Subdivision Name: | Japan |
| Subdivision Type1: | Prefecture |
| Subdivision Name1: | Tokyo |
| Subdivision Type2: | City |
| Subdivision Name2: | Nerima |
| Pushpin Map: | Japan Tokyo city |
| Coordinates: | 35.7633°N 139.5669°W |
| Population As Of: | August 1, 2008 |
| Population Total: | 13 |
is a small enclave district that belongs to Nerima, Tokyo, Japan, but is surrounded entirely by Saitama Prefecture.
Nishiōizumimachi is surrounded by Katayama 3-chōme, Niiza, Saitama, approximately north of Nishi-Ōizumi 6-chome. On August 1, 2008, there were six households in this district and its population was 13 (6 male and 7 female).[1] The area contains one small street running through the center. The entire area bears the number 1179 and individual houses are numbered 21, 23 and 25.
The exact date or reason for the exclave coming into existence is unknown, however it is theorised that it could be a remnant of a number of municipal mergers since the Meiji era.[2] The exclave went unnoticed until a property developer wanted to turn the then farmland into housing discovered the anomaly in 1974.[3] It is thought that the land may have been a field or falconry whenever the exclave was established.[4]
Administratively, Nishiōizumimachi is looked after by both Nerima and neighbouring Niiza. Water and sewage is handled by Niiza, whereas garbage disposal is handled by Nerima. Students in the exclave must also attend elementary and junior high school in Nerima. Residents have called Nishiōizumimachi's governance "inconvenient".[5]