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 | Malaysia, Cameroon, China, Tanzania, India |
| Bilay | Philippines, Senegal, Gambia, Myanmar, India |
| Bilaj | Germany, Greece, United States, Albania, India |
| Билай | Kyrgyzstan, Russia, Belarus, Kazakhstan, Ukraine |
| билай, вера иосифовна Ukrainian mycologist, UA (b. 1908) |
|