Here Mudassar Khan has explained how to install AJAX Control Toolkit in ToolBox of Visual Studio.
Supported versions: 2008, 2010, 2012, 2013, 2015, 2017, 2019, 2022 and higher.
AJAX Control Toolkit Library is not integrated in Visual Studio by default and hence I will explain a permanent way to add AJAX Control Toolkit controls to ToolBox in Visual Studio 2008, 2010, 2012, 2013, 2015, 2017, 2019, 2022 and higher versions.