Federation members

As of December 2380, there were 155 Member States of the United Federation of Planets, and Federation space spanned over 10,000 light years. 
 * See also Federation Colonies.

Founding member states
The United Federation of Planets was founded in 2161 by the governments of Earth (United Earth), (Confederacy of Vulcan), Andor (Andorian Empire), Tellar, and the independent Human colony of Alpha Centauri, all of which were previously members of the Coalition of Planets (though other members of the Coalition did not join the Federation initially). 


 * The novel Starfleet: Year One, published before Enterprise canologically confirmed the founding members of the Federation, gave eight founding worlds; Earth, Vulcan, Andor and Tellar remain, Alpha Centauri is omitted and Osadj, Dedderai, Vobilin and, last to agree to join, Rigel IV, are added. While these extra worlds could still be early members of the Federation, the majority of sources, and canon, now rule them out as founding members.