People over 65 narrowly outnumbered children under 15 for the first time at the end of last year.
Out of the country's registered population of 51.7 million at the end of December, the elderly population stood at 6.996 million or 13.5 percent but the number of children at 6.916 million or 13.4 percent, Interior Ministry said on Wednesday.
Elderly people increased 3.26 percent and children dwindled 2.06 percent over the course of the year.
Back in 2008, the proportion of the elderly was 10.2 percent compared to 17.2 percent children. But the birthrate has dropped and the population aged rapidly since then. This is the first time there are fewer than 7 million children in the country.
The population between 15 and 64, which accounts for 73.1 percent of the entire population, stood at 37.8 million. The entire registered population grew by 166,878 over the year.
Gyeonggi Province saw the biggest population increase, mainly due to people moving away from inner Seoul, with 194,174, followed by the new administrative city of Sejong with 32,164 and South Chungcheong Province with 19,078. Seoul's population shrank apace by 91,565 and Busan's by 15,248.