A mountainous municipality located in the valley of the river from which town draws its name placed in the lap of the Hernio massif (1075 m). It borders with Zestoa, Aia, Asteasu, Larraul, Bidegoian, Albiztur, Beizama and Azpeitia and also has a small enclave to the south, in the neighbourhood of Santa Marina. It has a population of more than 600 people spread between the urban town and the neighbourhoods of Santa Marina, Arzallus, Erdoizta, Ezama, Ibarbia, Letea and Argisain. The first written records date back to 1027, although the earliest reference of the presence of settlers in the territory can be traced back to the Upper Palaeolithic period.
The most common economic activity of its inhabitants is agriculture and animal husbandry. Its best-known product is the Errezil apple noted for its delicious flavour and is also known with the names of "Ibarbia" or "Errege- Sagarra". The Errezil Apple Day is celebrated every year in December.
The patron saint festivities of this town are celebrating on San Martín day (11 November). The festivities of San Antonio (13 June) and Domingo Erkizia (28 September) are also worth seeing. The pilgrimages that are held in Mt Hernio on all Sundays in September, especially on the last Sunday are very famous.