Ashiya is located at the mouth of the Onga River in north-central Fukuoka Prefecture, and is part of the Kitakyushu metropolitan area.

Fukuoka Prefecture Ashiya has a humid subtropical climate (Köppen Cfa) characterized by warm summers and cool winters with light to no snowfall.

In the late Yayoi period, the area was called "Oka no Tsu" and was famous as one of the three major military ports, along with Toyotsu and Usa.

At that time, it was a deep and vast bay, but due to the accumulation of earth and sand from the Onga River over the years and land reclamation, there is no trace of what it once was.

Ashiya has a mayor-council form of government with a directly elected mayor and a unicameral town council of 12 members.

In terms of national politics, the town is part of the Fukuoka 8th district of the lower house of the Diet of Japan.