In 2364, the USS Enterprise-D was en route to Pacifica for a scientific mission when Captain Jean-Luc Picard diverted it to Dytallix B for a secret meeting. Picard canceled the visit to Pacifica due to ensuing events, causing the leader of the planet, Governor Delaplane, to contact Starfleet Command. (TNG: "Conspiracy")
In 2365, a conference was held on Pacifica concerning the admission of the Antedians into the Federation. The Enterprise-D was assigned to transport an Antedian dignitary and his aide to the planet, as well as Ambassador Lwaxana Troi, on behalf of the Betazed government. She would state that she wished to marry William T. Riker on the shores of Pacifica's Western Sea, though she was affected by the Betazoid phase at the time. (TNG: "Manhunt")
According to Star Trek: Star Charts (p. 37) and Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), there was a star system named Pacifica, in which this planet might possibly have been located, in the Alpha Quadrant. The system's primary was a G-class star.