Ilo's name day is observed on November 18 in Estonia.
Ilo is a rare name in the USA, where it has little established history or widespread recognition. Originating primarily from the Finnish language, Ilo directly translates to "joy" or "happiness," lending it a remarkably positive etymology. The mood associated with Ilo is consequently bright, playful, and simple, characterized by an optimistic tone. Gender classification often leans masculine in Nordic regions but the name is frequently considered unisex worldwide due to its concise and gender-neutral structure. Its scarcity in American naming conventions places it firmly among unique and internationally inspired choices.
| Country | Day | Month | Names |
 France | 4 | January | Odilon |
 Greece | 13 | January | Ermilos |
 Czechia | 20 | January | Ilona |
 Slovakia | 23 | January | Miloš |
| Czechia | 25 | January | Miloš |
 Lithuania | 27 | January | Ilona, Jogundas, Jogunde, Natalis, Vytenis |
 Poland | 27 | January | Angelika, Ilona, Jan Chryzostom, Julian, Przybysław |
| Lithuania | 5 | February | Agota, Birute, Gaudvinas, Ilona |
| Czechia | 17 | February | Miloslava |
| Slovakia | 17 | February | Miloslava |
| Greece | 19 | February | Filothei |
 Croatia | 3 | March | Anzelmo, Marin, Kamilo |
 Estonia | 8 | March | Viilup, Viilo, Vilbo, Lepo |
 Latvia | 18 | March | Adelina, Ilona, Razna, Sartite |
| Lithuania | 20 | March | Filomenas, Imgarda, Irma, Tautvile, Zygimantas |
| Estonia | 23 | March | Aksel, Ailo |
| Latvia | 21 | April | Anastasija, Margers, Margonis, Nilola |
 USA | 30 | April | Miles, Milo, Myles, Ryder |
 Bulgaria | 21 | May | Elena, Konstantin, Kosta, Kostadin, Kostadinka, Lenko, Dicho, Lenko, Dinko, Elenko, Eli, Elin, Elka, Ilona, Kojcho, Kostadina, Kostadinko, Kuncho, Stamen, Stanimir, Stanimira, Stanka, Stoil, Stoyan, Stoian, Stoyanka, Trayko, Dinko |
| USA | 1 | June | Brigham, June, Junella, Marilee, Marilou, Marilu, Marilyn, Marylynn |
 Spain | 12 | June | Nazario, Olimpo, Cirilo |
| Spain | 27 | June | Socorro, Zoilo, Ladislao, Anecto, Sansón |
| Lithuania | 5 | July | Butginas, Filomena, Karolina, Mantmile |
| Poland | 5 | July | Antoni, Bartłomiej, Filomena, Jakub, Karolina, Michał, Przybywoj, Szarlota, Wilhelm |
| Spain | 5 | July | Filomena, Filomeno, Zoa |
| Greece | 8 | July | Theofilos, Prokopios |
| Slovakia | 11 | July | Milota |
| Croatia | 14 | July | Kamilo de Lellis, Miroslav |
| Spain | 14 | July | Camila, Vladimiro, Camilo |
| Bulgaria | 20 | July | Iliya, Iliyana, Ilko, Ilina, Ilka, Lilo, Lila |
| Poland | 10 | August | Asteria, Bernard, Bogdan, Borys, Filomena, Laurencjusz, Prochor, Wawrzyniec, Wierzchosław |
| Spain | 11 | August | Clara, Filomena, Susana |
| Estonia | 18 | August | Heleene, Helene, Helena, Elina, Ilona, Helen, Hell, Hella, Helle, Hellen, Helli |
 Hungary | 18 | August | Ilona |
| Lithuania | 18 | August | Gendvile, Ilona, Mantautas, Sailenis, Saulene |
| Poland | 18 | August | Agapit, Bogusława, Bronisław, Bronisz, Helena, Ilona, Klara, Tworzysława |
 Finland | 7 | September | Miro, Arho, Arhippa, Milo |
| Spain | 19 | September | Nilo |
| Finland | 9 | October | Ilona |
| Croatia | 8 | November | Gracija Kotorski, Milotislav, Bogdan |
| Greece | 10 | November | Milon, Orion |
| USA | 22 | November | Abbey, Abbie, Abby, Abigail, Cecelia, Cecil, Cecilia, Cecily, Cecyl, Celia, Gael, Gail, Galen, Gay, Gayle, Philemon, Philo, Shayla, Sheila |
| Estonia | 6 | December | Nigulas, Nigul, Nikolai, Niilas, Niilo, Nils, Klaus, Laas, Laus |
| Finland | 6 | December | Niilo, Niko, Niki, Nikolas, Niklas, Nikolai, Niila |
 Austria | 11 | December | Arthur, Damasus, Tassilo |
| Latvia | 14 | December | Auseklis, Dailonis, Gaisma |
| Czechia | 18 | December | Miloslav |
| Slovakia | 27 | December | Filoména |