The earliest settlers came to settle at Yoshinogari site sometime before 400 BC.
They evidently found the site a good location for building a permanent village, for Yoshinogari was situated on top of a ridge in the foothills of the Sefuri Mountains, a mere 12 km from the Ariake Sea and most importantly, the location was surrounded by land on three sides that was suitable for cultivating rice.
The early settlers built a moated settlement that was about 2.5 hectares in area. They built there a small number of pit houses, and surrounded their village with ditches. They dug storage pits and buried their dead there in burial jars.
By the Middle Yayoi period, the village had expanded in size to about 20 hectares in area. The villagers must have become somewhat prosperous for they built large wooden raised-floor grain storage houses (or granaries) in the middle and southern areas of the site. The largest building was 12.5 m by 12.5 m with huge wooden posts 40-50 cm in diameter.
The villagers also dedicated a special area of the village to crafts such as the casting of bronze objects and the making of pottery (of a kind that is similar to pottery found along the coastal areas of Korea). Archaeologists think that the villagers had strong contacts with Korean peninsula during this time perhaps in relation to interchanges with Korean bronze-casting specialists.
Funerals and rites for the dead appeared to have been important and elaborate to the villagers, especially where members of the village of an elite status were concerned. In an area quite separate from the communal cemetery for commoners, a 30 by 40 m mound was constructed where the village chiefs and leaders were buried. Five of the six jars found in the centre of the mound contained cylindrical jade-like glass ornaments from China as well as bronze daggers that came from the Korean peninsula.
For the commoners, they built a cemetery containing long rows of jar burials. About 2,000 burial jars, have been found both inside and outside the ditches. Inside one of these jars with a stone lid, buried with a female body, was discovered a finely-made bronze mirror (7.4 cm in diameter with a pattern of interconnected arcs and a eight-character inscription) in the renkomon style of the Early Han Dynasty period). The female had been buried in silk clothes and wearing 25 shell bracelets on her right arm and eleven bracelets on the left. The shell bracelets were exotic items, made from cone shells from the south seas and must have shone beautifully like pearls when they were first worn.
Other items excavated from Yoshinogari include Japanese-style bronze mirrors, coins, bells, halberds, iron tools and wooden tools.
During the Late Yayoi period, the village had grown to an enormous 40 hectares. The defenses of the village had also been expanded, to completely surround the settlement and cemetery areas. Multiple defensive ditches were built, with the large outer ditch around the edges of the low hill and smaller ditches surrounding the pit houses and raised-floor buildings. There were even double ditches encircling the northern area. Palisades were built on the inside of the ditches.