The city is located at . 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.
Excavations in 2008 for a tunnel bridging the Coatzacoalcos River indicate a substantial pre-hispanic population. By the time of the Spanish arrival the area was under Mayan influence. In 1522, Hernán Cortés ordered Gonzalo de Sandoval to fund a settlement near Guazacualco. Sandoval named it Villa del Espíritu Santo. It was elevated to the category of port in 1825 and the name changed to Coatzacoalcos.
In 1900 the name was changed to Puerto México. In 1911 it was elevated to city, and in 1936 the name was changed to the current Coatzacoalcos.
Coatzacoalcos became a very important crossroads during the oil boom of the 1970s, connecting the Yucatán Peninsula and oil fields in Campeche to the rest of Mexico and to the port of Salina Cruz in Oaxaca on the Pacific coast.
The city's industry is dominated by the petrochemical sector. Four big industrial petrochemical complexes are located near the city (Pajaritos, Cosoleacaque, Morelos and Cangrejera) making it one of the most important concentrations of its kind in the world. The state-owned Pemex Petroquímica is headquartered in Coatzacoalcos and 85% of its production is concentrated there.
Coatzacoalcos, in Nahuatl language, means "The place where the snake hides" According to the legend, this is the place where the god Quetzalcoatl made his final journey to the sea around the year 999 and where he made his promise to return.