Lagny-sur-Marne Population and Area (Seine-et-Marne)

Lagny-sur-Marne: Population and Area

With 21,673 inhabitants (INSEE total population in force on January 1, 2026), Lagny-sur-Marne is the 440^th most populous town in France in 2026 and the 14^th most populous in the Seine-et-Marne department, out of 507 communes. It covers 5.72 km² (27,958^th largest area in France, 405^th largest in the department), with a population density of 3,789 inhabitants per km², or 35 times the national average (110 inhabitants/km²), which ranks it 214^th in France for density.

Lagny-sur-Marne is located in the Seine-et-Marne department (77), in the Île-de-France region, where it ranks 162^nd by population out of 1,266 communes. The most populous town in the Seine-et-Marne department is Meaux (57,360 inhabitants); the department is home to 1,484,180 people over 5,915 km².

See the full ranking of communes in the Seine-et-Marne department and the regional ranking: largest city in Île-de-France.

Towns of similar size in the Seine-et-Marne department: Roissy-en-Brie (pop. 23,370), Torcy (pop. 22,941), Montereau-Fault-Yonne (pop. 22,467), Ozoir-la-Ferrière (pop. 21,422), Mitry-Mory (pop. 20,525), Le Mée-sur-Seine (pop. 19,658).

Sources: INSEE, official population figures in force on January 1, 2026 (total population); areas: IGN / Observatoire des territoires; INSEE code 77243. Rankings are calculated across the 34,858 communes of metropolitan and overseas France in our database.