Isidor’s name day is February 4, the feast of Isidore of Pelusium.
Churches that follow the Old (Julian) Calendar keep the same feast on February 17 of the civil calendar. See everything commemorated on February 4.
The saint behind the name

Isidore of Pelusium
February 4, Venerable, Ισίδωρος
St. Isidore of Pelusium was an ascetic of Egypt in the fifth century, who lived in monastic retirement near the city of Pelusium at the mouth of the Nile. A man of wide learning and deep devotion to the Holy Scriptures, he revered the teaching of St. John Chrysostom and followed his example of bold and clear instruction.
Also celebrating on February 4
These names share the feast, many of them other forms of the same name:
What to say on a name day
The Greek wish is Χρόνια Πολλά (Chronia Polla), “many years.” A call or a short message on the day is what people remember. See name day wishes you can send and what a name day is.