Illondia, also called the "Seahills of the Snoutridge" or colloquially the "Seahills", was the northernmost Common League region. Disconnected from mainland Commona by the Snoutridge Mountains and insulated by Wyrmhorn Gulf, Illondia was historically a Human-majority land composed of small fishing, farming, and mining communities. Rivers, beaches, and coves were abundant as the hills reached the bay, but its few flats were still arable enough to sustain agriculture. Many residents of the Seahills claimed distant Elven heritage, as the lands had once been occupied by the elves of the Forests of Mana Thalor in the Age of Giants; however, only a minority manifested Fey-like qualities.
Though Illondia shared a similar culture to much of Commona and paid dues as member of the League for protection, the communities of the Seahills considered themselves semi-independent. Historically, settlements in the region faced constant threats from raiders from the mountains, pirates from the Siren's Isles, and armies from noble houses in , leading to a culture of independence. In times of need, they often relied on help from the Kingdom of the Twelve Mountains or of Ardhon Miniel, as most Common forces were stationed on the other side of the mountain range.