Ermua has a population of around 16,000 people, making it a small yet vibrant community. The town has experienced gradual growth over the past few decades, largely driven by its proximity to larger industrial centers. The majority of residents are Basque, and Euskara, the Basque language, is commonly spoken alongside Spanish, giving the town a distinctly bilingual character.
The population is diverse in age, with a mix of young professionals, families, and older residents. While the town retains a strong sense of tradition, it is also home to a growing number of newcomers who have been attracted by its quality of life and employment opportunities in nearby cities.