The Klingon system was the star system where Qo'noS, the capital of the Klingon Empire, was located. The system was located less than ninety light years from the Sol system, and an NX-class starship could travel between them in four days at warp 4.5. (ENT: "Broken Bow", "Two Days and Two Nights")
The star of the system was first seen in TNG: "Redemption" as the USS Enterprise-D and IKS Bortas approached Qo'noS. According to the Starfleet Medical Reference Manual, the Klingon homeworld was the planet "Epsilon Sagittarii B". Epsilon Sagittarii is a real star located 143 light years away from Earth. According to the Star Trek: Star Charts (page 56), the star was an orange dwarf located in the Beta Quadrant. Star Trek Maps and The Worlds of the Federation name the star as "Klingon".