
These are species with at least one recorded territory in South Korea, not a national checklist: a bird list from eBird or Avibase is more complete. The counts follow recording effort as much as wildlife, so a country with more visitors and more naturalists will show more of both.
The species with the most open occurrence records in South Korea, among those a photograph exists for. Most recorded is not most numerous: it rewards animals that are common, conspicuous and live where people go.

Pica serica

Hypsipetes amaurotis

Streptopelia orientalis

Parus cinereus

Anas zonorhyncha

Suthora webbiana

Larus crassirostris

Aegypius monachus

Phoenicurus auroreus

Passer montanus

Cyanopica cyanus

Corvus macrorhynchos
The reference database has no regions filed under South Korea.
The field guide covers South Korea on the map, but none of its species have an entry written for them yet.