Quirinus Johan Harder (13 October 1801 in Rotterdam – 21 October 1880 in Vlissingen) was a Dutch architect best known for having designed a large number of lighthouses.
He worked as a structural engineer for the Loodswezen, the Dutch organization overseeing all maritime pilots.
Harder's lighthouses were made of cast iron, a new material at the time, which allowed for segmented fabrication and construction.