Who Was the First and Why?

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The probate of Belinda Newman in Linn County, Iowa, indicated three children were in Hancock County, Illinois.

My ancestor and at least three of his siblings spent some time in Hancock County, Illinois, during their life. Two of his siblings died there.

To the best of my knowledge his parents never lived there and some of his siblings went from Indiana straight to Iowa without making any long-term stops in Illinois. The family originally lived in Indiana where the children grew up and where the father died in 1864.

The question is: who was the first one to move to Hancock County, Illinois? What brought them to that area? Were there more distant relatives living in the area already? Were there others from the same Indiana location who moved to the same Illinois county? Or did one just settle there for reasons that can’t now be precisely determined and others simply followed?