In the Nebraska license plate system, Lancaster County was represented by the prefix 2 (indicating that it was the second most populous county when the license plate system was established in 1922). In 2002, the state abandoned this number system in the three largest counties.
According to the U.S. Census Bureau, the county has a total area of 2,193 km² (847 mi²). 2,173 km² (839 mi²) of it is land and 20 km² (8 mi²) of it is water. The total area is 0.92% water.
As of the census2 of 2000, there are 250,291 people, 99,187 households, and 60,702 families residing in the county. The population density is 115/km² (298/mi²). There are 104,217 housing units at an average density of 48/km² (124/mi²). The racial makeup of the county is 90.07% White, 2.82% Black or African American, 0.64% Native American, 2.86% Asian American, 0.06% Pacific Islander, 1.69% from other races, and 1.87% from two or more races. 3.37% of the population are Hispanic or Latino of any race.
There are 99,187 households out of which 30.30% have children under the age of 18 living with them, 48.80% are married couples living together, 9.10% have a female householder with no husband present, and 38.80% are non-families. 29.10% of all households are made up of individuals and 8.30% have someone living alone who is 65 years of age or older. The average household size is 2.40 and the average family size is 3.00.
In the county the population is spread out with 23.50% under the age of 18, 15.40% from 18 to 24, 30.40% from 25 to 44, 20.30% from 45 to 64, and 10.40% who are 65 years of age or older. The median age is 32 years. For every 100 females there are 99.80 males. For every 100 females age 18 and over, there are 98.50 males.
The median income for a household in the county is $41,850, and the median income for a family is $53,676. Males have a median income of $34,720 versus $25,614 for females. The per capita income for the county is $21,265. 9.50% of the population and 5.50% of families are below the poverty line. Out of the total people living in poverty, 9.90% are under the age of 18 and 6.10% are 65 or older.