Herilia, designated P4X-552 of Tau'ri was a planet in Milky Way galaxy which has a Stargate. Herilia is farther from its sun than Earth, making it a world struggling to reach dusk at full noon. This lack of sunlight is offset by the runaway greenhouse gas emissions, making it a habitable, but weakly, world. Residents have adapted over generations, these conditions, but the agents are likely to find the place a bit more difficult to navigate.
In this world, a Goa'uld called Diancecht sowed a group of people of Celt descent. Herilians threw out his regime in a bloody insurgency centuries ago, taking advantage of the fact that Diancecht resources were spread thin at the time because of a particularly bloody war with another System Lord. (RPG: "The Herilian Agenda")