Nakoku (奴国 Nakoku, Na no Kuni ) was a state which was located in and around modern-day Fukuoka City, on the Japanese island of Kyūshū, from the 1st to early 3rd centuries. Much of what is known about it comes from ancient records of both China and Japan.
According to the Book of Later Han, in 57 CE, Emperor Guangwu of Han granted Nakoku an imperial seal, patterned after the Chinese jade seals, but made of gold. In return, that same year, Na sent envoys to the Chinese capital, offering tribute and formal New Year's greetings. This seal was discovered over 1500 years later, by an Edo period farmer on the island of Shikanoshima, thus helping to verify the existence of Nakoku, which was otherwise known only from the ancient chronicles. Engraved upon it are the characters 「漢委奴國王」(kan no wa no na no koku-ō, King of the Japanese country of Na of Han).
A reference is found in the Gishiwajinden (魏志倭人伝, Records of Wei: Biography of the Wa people), a portion of the Chinese Records of the Three Kingdoms, to the continued existence of Nakoku in the 3rd century, naming the officials and stating that it contains over 20,000 homes.
Some believe that Nakoku may correspond as well to "Na no agata" (儺県), a principality which preceded Fukuoka City.
Notes and references 
- The character 国/國, read as koku or kuni in Japanese, can be translated as "country" or "province"
- Much of the content of this article is derived from that on the corresponding article on the Japanese Wikipedia. Transcriptions of the relevant portions from the ancient texts can be found there as well.
- Frederic, Louis. "Nakoku." Japan Encyclopedia. Cambridge: Harvard University Press, 2002.