Calbayog City is situated on the western part of Samar, bounded on the north by Catarman, Mondragon, San Isidro and Pambujan, on the east by Sta. Margarita and Gandara, and on the west and south by the Samar Sea. It has 157 barangays.

The city has a land area of 903 square kilometers. In 1995, it had a population of 129,616. The dialect spoken by the Samareños is Samar-Leyte (Waray). Some people believed that the word Calbayog was derived from the combined words cal (the Spanish word for lime) and bayog (tree from which lime is extracted).

The others, however, believed it was derived from Kan Bayog, meaning, Bayog's place. The forerunner of Calbayog settlement was Caybago. From here, the inhabitants moved to Anislag, which was found to be unsafe, because it was always visited by flood.