La Unión de Isidoro Montes de Oca is a municipality in the Mexican state of Guerrero. The municipal seat lies at La Unión. The municipality covers an area of 1,142 km (441 sq mi).

As of 2005, the municipality had a total population of 25,230.

The main towns are La Unión, population 3,079; Petacalco, population 2,671; Zacatula, population 1,417; Lagunillas, population 1,371; El Naranjito, population 1,167; and Surcua, population 1,046.

History

On October 26, 1614, the Dutch Captain Joris van Spilbergen - involved in his country's war with Spain - raided with an expedition of five ships this part of the coast of the then Spanish Mexico. At Zacatula he captured the pearl fishing ship San Francisco.