Oeiras is a town and municipality in the western part of Lisbon metropolitan area, located within the Portuguese Riviera, in continental Portugal. The municipality is part of the urban agglomeration of Lisbon and the town of Oeiras is about 16 km from Lisbon downtown. The population in 2011 was 172,120 living in an area of 45.88 km2, making the municipality the fifth-most densely populated in Portugal.