Ōi (大井町, Ōi-machi) was a town located in Iruma District, Saitama Prefecture, Japan.

It's old Oi village hall with Oi elementary-school in fujimino-city.

As of 2003, the town had an estimated population of 47,276 and a population density of 6,014.76 persons per km2. The total area was 7.86 km2.

On October 1, 2005, Ōi, along with the city of Kamifukuoka, was merged to create the city of Fujimino.

35°51′04″N 139°31′01″E / 35.851°N 139.517°E / 35.851; 139.517