Are you talking about new construction or existing homes? Around $100/sq foot sounds dirt cheap to me. Are you talking with or without land and basement? Wholesale or retail?
Off the top of my head, I recall a figure of about $85/sq ft for materials and labor in the Chicagoland area a couple years ago as a wholesale price without a General Contractor's fee or the cost of land.
In Peoria, you can buy an existing 650 sq ft home for just $75/sq ft.
In Kenilworth the average cost per sq ft for existing homes is $536. Where a 4500 sq ft home might be $650/sq ft and a 2800 sq ft home would be $400/sq ft.
As Patti said, it's too broad of a question.