Coatzacoalcos is a major port city in the southern part of the Mexican state of Veracruz, on the Coatzacoalcos River. Coatzacoalcos comes from an indigenous word meaning "Site of the Snake" or "Where the snake hides". The city serves as the municipal seat of the municipality of the same name.

The city is located at 18°09′N 94°26′W18.15°N 94.433°W. It is connected by road and rail to the Pacific Ocean about 160 km away. This location has prompted plans for an interoceanic waterway across the Isthmus of Tehuantepec, or for a much expanded railroad system, for over a century.

The city had a 2005 census population of 234,174, making it the third-largest city in the state after Veracruz and Xalapa, but first in metropolitan population. The municipality covers a surface area of 471.16 km² (181.916 sq mi) and reported a population of 280,263 persons. The largest community in the municipality, aside from Coatzacoalcos, is the town of Allende, with a population of 20,501.