Henry Trimen (26 October 1843–16 October 1896)  was a British botanist. He named several plants in the Dipterocarpaceae family.
He was born in Paddington, London, England, the son of Richard and Marinne Trimen and the younger brother of entomologist Roland Trimen. He graduated from King's College School, London and from King's College Medical School, Edinburgh, but never practiced medicine. He was the curator of the medical museum at King's College, London, and lecturer on Botany at St Mary's Hospital Medical School from 1867 to 1872. He joined the botanical department of the British Museum in 1869. He was the director of the Royal Botanic Gardens in Ceylon (now the Botanical Garden of Peradeniya, Sri Lanka) for sixteen years. While there, he founded the Museum of Economic Botany and also created subsidiary Gardens at Badulla and Anuradhapura. His major work at this time was The Flora of Ceylon, which was finished by others after his death. He became Fellow of the Royal Society in 1888. He was also a Fellow of the Linnean Society of London. He died in Kandy in 1896.