Cortland is an incorporated town in DeKalb County, Illinois, United States.

Only the towns of Cicero and Normal are larger, in terms of population.

As of the 2020 census[8] there were 4,398 people, 1,419 households, and 939 families residing in the town.

There were 1,561 housing units at an average density of 426.85 per square mile (164.81/km2).

21.35% of all households were made up of individuals, and 5.85% had someone living alone who was 65 years of age or older.