Geography. Muskiz is located in the valley of the Barbadum river. It is spread over a mountainous area corresponding to the core of the so-called anticline of Bizkaia, out of which erosion was brought about a transversal valley. The highest mountains are: Mello (630 mts), Peña Corbera (361 mts), Pico Carrascal (269 mts), Pico Ramos (229 mts) and Janeo (203 mts)
The Barbadun river flows through it and forms the estuary of Pobeña at its mouth. The Barbadun river receives on its way to the sea several streams and the Cotorrio river.
Borders. The township of Muskiz borders on the Bay of Biscay to the North, on the township of Zierbena and Abanto to the East, on Castro Urdiales ( Province of Cantabria) to the West and on the townships of Galdames and Sopuerta to the South.
Composition. San Juan is the capital in which is concentrated aproximately 77% of the whole population. Other population centres are: Kobaron ( 4'5 Kms away from San Juan), Pobeña ( 4'1 Kms away), La Rigada ( 2'5 Kms away), San Julian ( 1 Km away) and Santelices ( 1 Km away).
Population. The mining wealth of this area, nowadays in decline, made it possible for Muskiz to always count on an important population level maintained along the years. The expansion of the urban-industrial area of Bilbao towards the West, Muskiz being fully integrated in it, caused a rise in population that has stopped over recent years.
Demographic evolution in Muskiz:
| Year | 1900 | 1910 | 1920 | 1930 | 1940 | 1950 | 1960 | 1970 | 1978 | 1981 | 1991 |
| Number of inhabitantes | 2831 | 4040 | 4102 | 4424 | 3746 | 4042 | 4761 | 6011 | 6184 | 6010 | 6425 |
| 0 - 19 years | 1662 | 26,1% |
| 20 - 64 years | 3828 | 60,2% |
| 65 onwards | 868 | 13,7% |
Primary Sector. It counts for 1' 6% of the employed people. The ruggedness of the area only leaves 4' 9% of the land workable, most of which is dedicated to the growing of forage and meadowland. The number of agrarian exploitations is even decreasing due to the prosperity of the industrial and urban installations.
Industry and Construction It composes 54% of the employed population. It has great importance but only regarding the level of employment of the population. The industrial installations Muskiz has, apart from the refinery of Petronor, are concentrated in small metal and wood workshops. In 1972 the refinery of northern oil (Petronor) was inaugurated, whose industrial complex is located in the Barbadun valley. It has also a pipeline from the port of Bilbao in the area of Santurce. The influence of this installation goes beyond the regional borders, supplying not only the whole industrial area of Bilbao but the whole of Euskadi and areas based along the main routes leaving from the North.
Service Sector It counts for 44' 29% of the employed population. Although they consist of an important % of the employed population, they are not highly specialized. They deal with basic necesities. Good communications with the urban zones of the area hinder the presence of a bigger trade.
Links Muskiz has traditionally been well linked to the other townships of the county. It is crossed by the national road 634 (From Bilbao to Santander). The building of the highway joining both capital cities has further improved these links. On the other hand, both the Renfe train service and the Bizkai-Bus bus service keep up regular links to the township.
| Service | Address | Phone | Fax |
| City Hall | San Juan, 2 | +34 4 670.60.00 | +34 4 670.63.63 |
| Kultur Etxea | Cendeja, 29 | +34 4 670.70.75 | +34 4 670.72.75 |
MUSKIZ
is a full member of Bilbao
Metropoli-30.