The Miami Valley, broadly, refers to the land area surrounding the Great Miami River in southwest Ohio, USA, and also includes the Little Miami, Mad, and Stillwater Rivers as well. Geographically, it includes Dayton, Springfield, Middletown, Hamilton, and other communities.
According to an article in the Cincinnati Enquirer, as Greater Cincinnati grows northward through Butler County, it is expected to eventually merge with Greater Dayton by 2010, thereby virtually erasing any distinguishable boundary between the two current Metropolitan Statistical Areas (MSA). As a result, the US Census Bureau will begin reporting the Cincinnati and Dayton metropolitan areas as one by that time. The new Cincinnati-Dayton metroplex will be comparable in nature to that of Baltimore-Washington's and place it within the top 20 most populous metros in the US with a population of nearly 3.1 million.http://news.enquirer.com/apps/pbcs.dll/article?AID=/20070311/BIZ01/703110330