AjaxControlToolkit.dll missing from Bin folder

Hi,

Running Visual Studio 2012 Express Edition

I have placed ScriptManager in correct position in aspx but no AjaxControlToolkit.dll appears in Bin folder

When trying to run, I get error:

- The type or namespace name 'AjaxControlToolkit' could not be found (are you missing a using directive or an assembly reference?) -

I have recently added a reference to a class library I created with custom C# classes. I don't know if this is problem though.

I have tried adding reference to AJAX but didn't know where to find.

I guess I need to get AjaxControlToolkit.dll in Bin folder first. I did not know where to start.

Thanks.