If your .NET solution contains projects that contain custom/user controls for windows/web forms these controls are automatically loaded into the toolbox so that they can be utilized on your forms. In some cases when there are a large number of controls in your project the solution seems to compile slowly or the toolbox seems to take quite some time to load. If you are facing such issues turn off the AutoToolboxPopulate property on the ToolsàOptionsàWindows Forms DesigneràGeneral tab.