On January 1, 2006, Lierneux had a total population of 3,367. The total area is 92.08 km2 which gives a population density of 37 inhabitants per km2. Lierneux is known for its psychiatric hospital CHS l'Accueil.
Within the bounds of the municipality a lies a memorial site to the tribute of the 82nd Airborne Division who won the Battle of the Bulge against the German SS division December 22, 1944.