Ōmiya-ku is surrounded by Nishi-ku (to the west), Kita-ku (north), Minuma-ku (east), Urawa-ku (southeast), Chūō-ku (south), and Sakura-ku (southwest).

The modern town of Ōmiya was officially created within Kitaadachi District, Saitama with the establishment of the municipalities system on April 1, 1889.

On November 3, 1940 Ōmiya merged with the neighboring villages of Mihashi, Osato, Miyahara and Nisshin and was elevated to city status.

Ōmiya continued to expand after the end of the war, absorbing the villages of Sashiougi, Mamiya, Uemizu, Katayanagi, Haruoka, and Nanasato on January 1, 1955.

In April 2003 Saitama became a city designated by government ordinance, and now the area of former Ōmiya City was divided between Kita-ku (north), Minuma-ku (east), Nishi-ku (west), and Ōmiya-ku (south).