Lenexa's population was estimated to be 43,434 in the year 2005.
As of the U.S. Census in 2000, there were 40,238 people, 15,574 households, and 10,559 families residing in the city. The population density was 1,173.8 people per square mile (453.2/km²). There were 16,378 housing units at an average density of 477.8/sq mi (184.5/km²). The racial makeup of the city was 89.50% White,6.50% Black or African American], 0.38% Native American, 3.63% Asian, 0.03% Pacific Islander, 1.60% from other races, and 1.61% two or more races. Hispanic or Latino of any race were 3.97% of the population. 24.8% were of German, 12.4% English, 12.1% Irish and 7.2% American ancestry according to Census 2000.
There were 15,574 households out of which 35.1% had children under the age of 18 living with them, 57.4% were married couples living together, 7.6% had a female householder with no husband present, and 32.2% were non-families. 24.3% of all households were made up of individuals and 5.8% had someone living alone who was 65 years of age or older. The average household size was 2.54 and the average family size was 3.08.
In the city the population was spread out with 25.7% under the age of 18, 9.5% from 18 to 24, 32.0% from 25 to 44, 24.2% from 45 to 64, and 8.6% who were 65 years of age or older. The median age was 35 years. For every 100 females there were 95.8 males. For every 100 females age 18 and over, there were 93.1 males.
The median income for a household in the city was $61,990, and the median income for a family was $76,321 (these figures had risen to $70,246 and $86,581 respectively as of a 2007 estimate). Males had a median income of $50,495 versus $32,166 for females. The per capita income for the city was $30,212. About 1.8% of families and 3.4% of the population were below the poverty line, including 2.9% of those under age 18 and 3.0% of those age 65 or over.