Blue Horizon was a Federation planet terraformed by famed terraformer Professor Gideon Seyetik. His crowning achievement on the planet was Da Vinci Falls.
Commander Benjamin Sisko and his son Jake visited Blue Horizon on their way to Deep Space 9 in 2369. (DS9: "Second Sight")
According to the Star Trek: Star Charts, on the chart "United Federation of Planets I", Blue Horizon was listed as a member planet of the Federation in 2378.