Oulu is a city in Finland and the regional capital of North Ostrobothnia. It is located on the northwestern coast of the country at the mouth of the River Oulu. The population of Oulu is approximately 215,000, while the sub-region has a population of approximately 263,000. It is the 5th most populous municipality in Finland, and the fourth most populous urban area in the country. Oulu is also the most populous city in Northern Finland.