The City of Cortland, near the west border of the county, is surrounded by the Town of Cortlandville.
As of the census of 2000, there were 18,740 people, 6,922 households, and 3,454 families residing in the city. The population density was 4,778.6 people per square mile (1,845.8/km²). There were 7,550 housing units at an average density of 1,925.2/sq mi (743.6/km²). The racial makeup of the city was 95.72% White, 1.56% African American, 0.25% Native American, 0.57% Asian, 0.02% Pacific Islander, 0.56% from other races, and 1.33% from two or more races. Hispanic or Latino of any race were 1.72% of the population.
There were 6,922 households out of which 24.8% had children under the age of 18 living with them, 34.7% were married couples living together, 11.4% had a female householder with no husband present, and 50.1% were non-families. 36.0% of all households were made up of individuals and 13.0% had someone living alone who was 65 years of age or older. The average household size was 2.28 and the average family size was 2.95.
In the city the population was spread out with 18.3% under the age of 18, 28.4% from 18 to 24, 23.6% from 25 to 44, 16.8% from 45 to 64, and 12.9% who were 65 years of age or older. The median age was 28 years. For every 100 females there were 88.4 males. For every 100 females age 18 and over, there were 84.5 males.
The median income for a household in the city was $26,478, and the median income for a family was $39,167. Males had a median income of $29,857 versus $21,614 for females. The per capita income for the city was $14,267. About 13.9% of families and 24.7% of the population were below the poverty line, including 24.8% of those under age 18 and 15.2% of those age 65 or over.