I have seen the surname Whelan spelled in many different ways. Occasionally, it is spelled 2 or more ways in a single document.
Here are 21 alternate spellings of the name Whelan that I have found in my research. I'll add more as I come across them. If you have found one that I've missed, let me know and I will add it to the list.
Wallen, Whalan, Whaland, Whalen, Whalin, Whaling, Whallan,
Whallin, Whallon, Whalon, Whealan, Whealin, Whealon, Wheelan,
Wheelin, Wheeling, Whehlen, Whelan, Whellen, Whelon, Whilan
Sources: Chicago city directories through 1864