[1] He listed 22,399 species in his cabinets in 1837—at the time, the greatest collection of Coleoptera in the world.

In 1802, he began publishing a catalogue of his vast collection, including 22,000 species names.

Dejean acted accordingly and often introduced in litteris names, given by himself to replace those already published by other authors.

Dejean was president of the Société entomologique de France for the year 1840.

In 1834, he was elected a foreign member of the Royal Swedish Academy of Sciences.