Ilarnek is a city in the land of Mnar on the River Ai in the Dreamlands. It was built by the same wandering tribes that built the Mnaran cities of Thraa, Kadatheron, and Sarnath. Early in their history, an important trade route was established between Sarnath and Ilarnek. Sarnath eventually conquered the neighboring cities and lands (including Ilarnek) and forged an empire. (HPL: "The Doom That Came to Sarnath")
After the destruction of Sarnath, the green stone idol of Bokrug, the Great Water Lizard, was found on the marshy lakeshore where the city once stood. The idol, which had been taken by Sarnath from the conquered city of Ib, was enshrined in the high temple at Ilarnek and was subsequently worshipped throughout the land of Mnar. (HPL: "The Doom That Came to Sarnath")
Ilarnek is a repository of lore pertaining to the beings of Ib written on papyrus, including their discovery of fire and their use of flame in rituals and ceremonies. (HPL: "The Doom That Came to Sarnath")