The Trill Diplomatic Corps was a Trill diplomatic body.
In 2075, a member of the Diplomatic Corps met with several Vulcans, including T'Pau, who wanted to speak to Lela Dax after the L'Dira attacked Trill. (DS9 - The Lives of Dax short story: "First Steps")
In 2376, the Trill Diplomatic Corps was involved in Bajor's admittance to the United Federation of Planets. Using his connections, Hiziki Gard was assigned to be Ambassador Gandres' aide by the Corps. (DS9 novel: Lesser Evil)