Six of the deaths were in Seoul, three in Gyeonggi and two in Gangwon, Yonhap News Agency reported, citing official data.
Three of the eight missing were also in the capital.
More than 3,770 homes and buildings were flooded, most of them in Seoul.
Authorities said some 4,300 people were evacuated from residences and other buildings, with nearly 1,000 being housed in temporary shelters in the capital.
According to the Korea Meteorological Administration, Seoul and its surrounding areas received around 525 millimeters of rain over three days.
The department lifted the downpour warning for Seoul and nearby areas but projected more heavy rain in South Korea's central parts, the report added.
