

周 (Zhou) is now the 10th most common surname in Mainland China, it has been one of the 10 most common surnames in China since the Yuan Dynasty (1271-1368). 周 was the fifth surname in the book 百家姓, a book of Chinese surnames first written in 960 A.D..
周 源出有四。
According to historical records, the Zhou surname dates back to the imperial kinsmen of the Zhou Dynasty (c. 1046 BC - 256 BC), which ruled China for 874 years. The original surname of the royal Zhou family was Ji. In 256 B.C., the Qin Dynasty conquered the Zhou Dynasty and put Rufen under the jurisdiction of Runan County. Ji Yong, a descendant of Emperor Ping of the Zhou Dynasty, which lived on the system of enfeoffment (investing nobility with hereditary titles) in Rufen, changed his surname to Zhou to commemorate the merits and virtues of his ancestors. The descendants of Emperor Nan of the Zhou Dynasty, who were called the Zhou family after the Zhou Dynasty had been destroyed, also took on the Zhou surname. Since then the Zhou surname has become a common family name in Runan.
During the reign of Emperor Xuanzong of the Tang Dynasty (618-907), the emperor issued an imperial edict to change the Ji surname to Zhou to avoid the taboo of his personal name. This was also a major source of the Zhou family name.
Apart from these roots, the change of surnames by ethnic minorities and Han people also contributed to the formation of the Zhou surname. For example, Emperor Xuanzong of the Tang Dynasty also changed the Ji surname, a different Chinese character but with the same pronunciation as the royal family name in the Zhou Dynasty, into Zhou. The Helu and Pu surnames of the Xianbei nationality in the Beizhou Empire (the Northern Zhou) and the Xitong and Shuhu surnames of the Mongolian nationality in the Yuan Dynasty were also changed into Zhou.
Passed down from the royal family in the Zhou Dynasty, the Zhou surname, of course, was extraordinary. People with the Zhou surname could be found all over the country due to enfeoffment and migration through the ages -- especially from Runan, the largest dwelling place for the Zhou family. Generally speaking, the migration of the Zhou family followed the pattern of "west to east" and "south to north". Later, people with the Zhou surname moved to Taiwan from the Fujian and Guangdong provinces.
Variants:
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