Today Apple unveiled iOS 9 in the WWDC (World Wide Developers Conference) 2015. So what devices will actually be supported to install and use iOS 9? The image below shows what devices can use iOS 9.
As stated above iOS 9 will work on the iPad 2, iPad 3rd generation, iPad 4th generation, iPad Air, iPad Air 2 and iPad Mini 1/2/3. In essence all devices that supported iOS 8 will support iOS 9.