After the last ice age, during early and middle Jōmon period, most of the area which is now Kawaguchi was under sea level except for the area which is now Omiya Tableland. Ancient peoples living in this area left several shell middens, in which shells, Jōmon pottery, and pit houses have been discovered by archaeologists. Many Kofun period barrows were also found in Kawaguchi, however many have also been destroyed by urban development. From the Heian period onwards, Kawaguchi was part of Musashi Province. The name "Kawaguchi" appears in the Kamakura period chronicle "Gikeiki", but it is not proven that this name designated current area of Kawaguchi.