The range of Eurasian Coot Fulica atra in Japan has expanded gradually since the 1980s, and the numbers of coot wintering at several sites in Japan have increased. In this paper, we summarize the trends in coot numbers wintering in Japan and mainland East Asia. In Japan, wintering numbers of coot have increased in most regions, except in northern Chiba Prefecture. The increase began in the late 1990s or around 2000 at several water bodies in the Kanto, Chubu, Kinki and Chugoku regions of Honshu. It also increased in the mid-2000s at several water bodies in the Tohoku, Kanto, Chubu, and Kinki regions of Honshu, and perhaps also on the island of Kyushu. In China, huge numbers of coot overwintered at several sites in the lower Yangtze floodplain (e.g., Poyang Lake, Dongting Lake) and along the Jiangsu Coast near the Yangtze River mouth (e.g., Yancheng Nature Reserve, Hongze Hu Lake) during the 1990s. However, during the 2000s, no sites in China held more than 10,000 wintering coot. The number of coot wintering in coastal south China has also decreased. In South Korea, the number of wintering coot has increased especially since the mid-2000s. The increases in the populations of wintering coot in central and western Japan and in South Korea seem to be mainly as a result of changes in coot populations and/or habitats outside Japan. We suggest two possible causes: the breeding population of coot on the East Asian mainland may have increased, or some coot that used to overwinter in China may have begun wintering in Japan and South Korea.