Ōarai is a town located in Ibaraki Prefecture, Japan. As of 1 July 2020, it had an estimated population of 15,867 across 6,881 households, with a population density of 664 inhabitants per square kilometre (1,720 per square mile). The town covers a total area of 23.89 square kilometres (9.22 square miles).
A notable demographic characteristic is the age of its residents: 34.0 percent of the population was aged over 65 as of the same date.
The Japan Atomic Energy Agency operates a research center in Ōarai, which includes a number of nuclear research reactors, among them the Jōyō and High-temperature engineering test reactor facilities.