Gemulon V was to be the home of a Federation colony in the late 2350s, but the SS Santa Maria never reached its destination. Officially, it developed life support problems while traveling through the Orellius system and was forced to crash land on a planet, where the would-be colonists made a home for themselves before finally being discovered by Benjamin Sisko and Miles O'Brien over ten years later.
Background information Edit
This planet was only mentioned in dialogue.
"GEHM-you-lahn" was the pronunciation for this planet's name from the script pronunciation guide. 
However, "GHEMM-you-lon" was the pronunciation for this planet from StarTrek.com. This website stated that this planet, presumably M-class, orbited the star Gemulon. This star was located in a Federation sector adjacent to the Bajor sector.  
According to Star Trek: Star Charts (p. 46) and Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), Gemulon was a trinary system in the Alpha Quadrant. This system consisted of a G-class star, a K-class star, and a M-class star. This was an independent system.