Delos IV was the inhabited fourth planet in the Delos system. Lieutenant Adele Simmons, a crewmember aboard both the USS Enterprise-D and USS Voyager, was born on this non-Federation planet.
In 2352, Beverly Crusher interned under Dr. Dalen Quaice on this planet. (TNG: "Remember Me")
In 2369, this planet was listed on the chart USS Enterprise Personnel Database, which was seen on Jean-Luc Picard's PADD on aboard the Enterprise-D. (TNG: "The Chase", okudagram)
According to Startrek.com, there were two systems named Delos and this Delos IV was not the same planet as Brekka. 
According to the Star Trek: Star Charts ("United Federation of Planets I"), Delos IV was listed as a member planet of the Federation in 2378.
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