>However, all of the deserializing methods seems to return an object of type "X". I'm not interested in a new object; I want the existing object to be populated with the XML settings.

If each xml file is a different instance of the class, then returning a new instance seems like the correct thing to do.

Instead, if the xml file is just a configuration file that contains default values for your object, then you can use the System.ConfigurationSettings.AppSettings property to get default values from the app.config file and initialize the object properties in the constructor. Look at dynamic properties in Visual Studio. You will have to write your own code to persist the property values to app.config.