Ōmihachiman is located in central Shiga Prefecture, on flatlands along the eastern shore of Lake Biwa, and extending inland to the foothills of the Suzuka Mountains.

Shiga Prefecture Ōmihachiman has a Humid subtropical climate (Köppen Cfa) characterized by warm summers and cool winters with light to no snowfall.

During the Sengoku period, the warlord Oda Nobunaga built Azuchi Castle in the hills on the border with Higashiōmi.

[5] The town of Hachiman was established with Gamō District, Shiga with the creation of the modern municipalities system on April 1, 1889.

In 1905, an American architect William Merrell Vories came to Ōmihachiman as an English language teacher at commercial high school.