The Aggregation of Rigellian Systems was a government that existed within the Rigel system and was based on Rigel IV. It was a member of the United Federation of Planets and part of the General Assembly. (TOS novel: Dreadnought!)

Its not known how this government relates to the United Rigel Colonies, its possible that the Aggregation covered only several planets within the Rigel system whilst the United Rigel Colonies covered the entire system though the name suggests that it covers star systems outside the Rigel system.