Lillestrøm Sportsklubb is a Norwegian professional football club based in the city of Lillestrøm, just outside of the capital Oslo. Lillestrøm SK is a Norwegian football club based in Lillestrøm, playing in Eliteserien. The club was founded in 1917, after the merger of two local football clubs. Their home ground is Åråsen Stadion, which has a capacity of 12,250 people, while the principal training ground is Lillestrøm stadion, or the indoor arena, LSK-Hallen. The club holds the Norwegian record for the most consecutive years without being relegated, having played 45 seasons from 1975 until 2019. Over the years the club has had around 40 players who have represented the Norwegian national team. There has also been a number of foreigners who have represented the national teams of the United States Sweden, Iceland, Senegal, Finland, Malta, Australia, South Africa, Slovenia, Tunisia, Canada, Somalia and Nigeria.

Lillestrøm is a municipality in Akershus county. It is located in the traditional district of Romerike. With a population of 85,757 inhabitants, it is the fourth most populated municipality in Viken. It was founded on 1 January 2020 as a merger between former municipalities Fet, Skedsmo and Sørum. The administrative centre of the municipality is the town of Lillestrøm. The town of Lillestrøm is a part of the Oslo metropolitan area.