I am working in Asp.Net using C# and I have a [WebMethod]
defined in a User Control. I don't want to use a web service.
How can I call a method with an [WebMethod]
attribute? I want to call it from a jQuery (Ajax) request.
You really should reconsider using a service if your goal is to centralize shared functionality.
ASMX services don't have any of the configuration burden that WCF services do (which is often what comes to mind when someone mentions "web service" now). If you use a simple ASMX "ScriptService", the code, development, configuration, etc will be nearly identical to what you're doing in ASPX files now, just centralized. ASMX ScriptServices and ASPX page methods are so similar that they literally share most of the same underlying backend code.