Incorporated on May 10, 1965, Lyndon became part of the new Louisville Metro government in 2003. It remains an independent city with its own mayor and emergency services and is not counted in Louisville's population although its citizens can vote for the mayor of Louisville and Metro Council members.
At some point after 1865, the L&N offered local landowner Alvin Wood connection to their network provided that he pay the costs of constructing the station and donated the land for the spur. He did so and, in 1871, the Lyndon depot began service. The town's etymology remains uncertain, although some connect it to Linn's Station and others to explorer William Linn.
There were 4,520 households out of which 21.9% had children under the age of 18 living with them, 37.5% were married couples living together, 8.9% had a female householder with no husband present, and 50.3% were non-families. 40.1% of all households were made up of individuals and 7.4% had someone living alone who was 65 years of age or older. The average household size was 2.02 and the average family size was 2.76.
In the city the population was spread out with 19.5% under the age of 18, 11.1% from 18 to 24, 38.3% from 25 to 44, 19.7% from 45 to 64, and 11.4% who were 65 years of age or older. The median age was 33 years. For every 100 females there were 97.0 males. For every 100 females age 18 and over, there were 95.1 males.
The median income for a household in the city was $42,974, and the median income for a family was $52,013. Males had a median income of $38,231 versus $27,886 for females. The per capita income for the city was $26,394. About 3.8% of families and 5.2% of the population were below the poverty line, including 3.9% of those under age 18 and 8.6% of those age 65 or over.