The Newberry Library in Chicago has created a remarkable tool to visualize county boundary changes over time. The site allows the viewer to use map layers to picture how county boundaries fluctuate. We all know how important it is to know where an ancestor is located in time to determine where needed documents are located. This site gives it to in one visual masterpiece. I have used it about ten times today: Atlas of historical county boundaries the link is also listed under "Contiguous State Online Indexes" (why do I call it that?!!).