Heiko or Henry Janssen, Illinois

Hi there,
I'm just starting out in my geneology of the Janssen family and I'm looking for any information I can get. My grandfather was Walter Janssen, his father was Henry Janssen, and his father was Heiko Janssen. Heiko allegedly came from Germany and settled in what is now Iriquois County, Illinois (specifically, the town of Buckley, Illinois).
Thanks for your help!
Scott Janssen