Hamlin was a Federation outpost, a colony settlement by the early 24th century.
History and specifics
Circa the 2310s decade, Hamlin was attacked by unknown assailants, later revealed to be Choraii. The entire colony was destroyed, with all adults killed. Many children were stolen by the Choraii, and were raised aboard their ships suspended in breathable oxygen liquid, kept partially drugged. Starfleet initiated secret missions to try and barter for the return of these children. (TNG novel: The Children of Hamlin)