The Korea Times has a pretty good graphic that shows the total number of foreign residents and where they live in Korea:

The number of foreigners based in Korea has exceeded one million for the first time, up 24 percent, or 215,543, from the previous year, a survey said Wednesday.

According to the one-month study conducted in May by the Ministry of Public Administration and Security, there are currently 1,106,884 foreigners residing in the nation, accounting for 2.2 percent of the nation’s entire population of 49,593,665.

“The double-digit increase is attributable to the inclusion of overseas Koreans who have lived in Korea for an extended period of time,” a ministry official said. Previously, they were excluded from the survey.

More than 60 percent of the foreign population live in Seoul and its vicinity ? 30.3 percent reside in Seoul, 29.3 percent in Gyeonggi Province and 5.6 percent in Incheon.  [Korea Times]

It is not surprising that most foreign residents live in Seoul but the rest appears to be pretty well spread out across Korea.