Casperia Prime is a world located within the Federation.
The world was mainly known as a tourism location and was referred to as the "vacation capital of the Horvian Cluster". (DS9: "Change of Heart")
The planet was also a premier location for conferences. Starfleet Medical held a conference there is 2374. (DS9: "Inquisition")
In 2410, the President of the United Federation of Planets Annek Okeg visited Casperia Prime to think about whether he should run for office again. At the end of his visit, Okeg was picked up by the USS Crucial. (Star Trek: Phoenix-X: "Election Year")
Casperia Prime article at Memory Alpha, the canon Star Trek wiki.