Family name Koeslag (Koeslag 
) , all over the world, is a rare cognomen. The surname Koeslag is habitual in Netherlands, where it is quite a rare surname, Canada, where it is a rare surname, and New Zealand, where it is a very rare surname. Not in comparison with a country's population, it is the most numerous in Netherlands, Canada, and South Africa.
| VARIANT | COUNTRY |
|---|---|
| Koeslag | Netherlands, Canada, United States, Germany, South Africa |