Megacounties: The Boom Towns

No longer suburbs, not quite cities: welcome to megacounties

Insurance Underwriter Joann Murphy moved to Oak Brook, Ill., 25 years ago "for the quiet and the country." But now her home in Du Page County is bracketed by office buildings and a huge shopping mall. A 31-story tower obliterates the view of trees and grass from her windows; its construction, still in progress, has sent clouds of dust and bursts of noise into her home. Laments Murphy: "This is like living in downtown Chicago."

Well, not exactly. If Du Page and dozens of other fast-growing counties all over the U.S. are beginning to look like spread-out cities, most of their...