Boulogne-Billancourt (often called Boulogne or Boulbi) is a town in the western suburbs of Paris in France. Boulogne-Billancourt is a sub-prefecture of the Hauts-de-Seine département. It is in the Île-de-France region. Its population is around 106,000. Its land area is 6.17 km². Its population density is 17,877/km².