What is the origin of the Korean surname "Kim" ?

The last name Kim is the most common Korean surname. It makes up 22 percent of the Korean population, which is equivalent to almost 10 million people. In contrast, there are rare family names that number less than 1,000, such as Pung or Sop. For over 1,000 years, Koreans have maintained the unique system of using their regional bases as an important way to differentiate their identities. So most Kims almost certainly do not share the same bloodline.

There are 285 regional origins for the Kims, such as the Kyongju Kim clan and Kimhae Kim clan. Consequently, in order to find out the origin of a particular Kim, one would have to identify which clan they are descended from and research that particular clan.

Ok, now the long answer:

Most commoners in Korea did not begin to adopt surnames until the late 10th century. During the Three Kingdoms period, which lasted until the late seventh century, using surnames was a privilege given to a limited number of social groups such as royal clans and the aristocracy. Each of the ancient three kingdoms had, at most, 10 surnames such as Ko for the royal clans for Koguryo and Paekche, and Park, Sok and Kim for the three different royal clans of Silla.

King Taejo, launching the Koryo Dynasty in the early 10th century, bestowed his loyal followers with last names and distinguished their surnames by their regional bases, giving birth to the modern "ponkwan" system. Ponkwan refers to the regional distinction of surnames.

He also condemned a band of rebellious strongmen in the present-day Mokchon area of South Chungchong Province by giving them "animal" surnames of pig, horse, elephant and cow, and graced other loyal subjects by allowing them to share his own surname, Wang.

During the Choson Dynasty (1392-1910), most commoners, except for slaves and outcasts, had surnames, as registered in period tax documents and conscription lists.

Listed in an annex to the official history of King Sejong in the mid-15th century are 265 surnames, while those discussed in a late 18th century document on lifestyle total 298, including an array of defunct, archaic surnames of that time.

Toward the end of the dynasty, a growing number of affluent commoners and entrepreneurs, who belonged to the lower echelons of the social hierarchy, secretly bought the status of nobility and adopted "dignitary" yangban surnames.

Adopted under the influence of the Japanese imperialists who sought to control Korea more effectively, the monumental decree required all Korean nationals to register their full names and regional origins. At that time, those without surnames often adopted the surnames of their masters or were simply assigned one by recording officials.

Compared to China and Japan, Korea has a far smaller number of surnames, among which the "big four" surnames - Kim, Lee, Park and Choi - dominate the scene. The extremely populous China hosts countless surnames, and Japan is home to some 132,000 surnames, a figure that is beyond comparison with Korea, even when one takes into account that its population is twice that of Korea.

The big four surnames were adopted by commoners in the course of Korean history since these surnames were simply perceived to be of blue blood. These names were also sometimes bestowed upon loyal servants by royalty or nobility. The Kim and Park clans were royal clans of the ancient Silla Kingdom.