Leiderdorp is a town and municipality in the western Netherlands, in the province of South Holland near the city of Leiden. It had a population of 27,109 in 2019.
The municipality covers an area of 12.28 km² of which 0.70 km² is water. Leiderdorp has now become a suburb of the city of Leiden, although the Oude Rijn river and the Zijl river separate the two. The HSL-Zuid high-speed rail line between Amsterdam and Brussels crosses Leiderdorp in a tunnel.
It is one of the oldest towns in South Holland province and was a base for the Spanish army in the Eighty Years' War.