Ilyria VI was a planet in the Illyria system, homeworld of a Federation member civilization.
History and specifics[]
Ilyria VI had recently joined the Federation as of 2268 or 2269.
In 2268 or 2269, Harry Mudd visited Ilyria VI. He sold Starfleet Academy to the natives, a con that delivered him enough credits to "borrow" a transport and travel to Sirius IX, where he acquired love potion crystals.
He then returned to Ilyria VI and sold some of his crystals there, but they just made the natives sick, so he assumed the crystals were phony. The inhabitants charged him with swindling and illegal drug manufacturing.
In 2269, while on the hangar deck plotting an escape from the USS Enterprise, Mudd initially considered stealing a shuttle and plotting a course for Ilyria VI, which would get him out of sensor range quickly. (TAS - Log Three novelization: Mudd's Passion)