Cognomen Билай (Bilai 
, Bilay 
, Bilaj 
) , around the globe, is quite a rare family name. The cognomen Билай is habitual in Albania, where it is quite a rare surname, Cameroon, and Senegal, where it is a rare surname. Not in comparison with a country's population, the name is most common in India, Cameroon, and Albania. Also, Билай is the forename as well as the last name.
| VARIANT | COUNTRY |
|---|---|
| Bilai | China, Malaysia, Tanzania, India, Cameroon |
| Bilay | Gambia, Philippines, Senegal, India, Myanmar |
| Bilaj | Germany, United States, India, Greece, Albania |
| Билай | Kazakhstan, Russia, Kyrgyzstan, Belarus, Ukraine |
| билай, вера иосифовна Ukrainian mycologist, UA (b. 1908) |
|