Celaya is a city and its surrounding municipality located in the southeast quadrant of the state of Guanajuato, Mexico. It serves as the municipal seat for an area covering 553.1 km2 (213.6 sq mi), which includes several outlying communities such as San Miguel Octopan, Rincón de Tamayo, and San Juan de la Vega.
The city is situated in the geographic center of its municipality. According to a 2005 census, Celaya had a population of 310,413, making it the third most populous city in the state of Guanajuato. The total population of the surrounding municipality was recorded at 415,869 during the same period.