I also have a great grandfather with the name Ilko, from Mycow area of Galacia (present day border of Lubelskie, Poland and Lviv, Ukraine). He most definitely identified himself as Ukrainian. I have records which show his name as Elko, Ilko, Ilza and
Elias. His marriage record, which appears to be in his own writing, shows his name as
Elias. None of my relatives ever recall his name being
Elias. Ilko is possibly a short form of
Elias?