How to pass one more parameter in ajax?

$.ajax({
    type: 'POST',
    url: '@Url.Action("SetDisplaySettings", "DisplaySettings")',
    data:$('#Form1').serialize(),
    success: function (result) {
        $('#chkIsSystemDefault').prop('checked', false);
        if(result=="2"){
           showAlertBox("Display Settings updated.");   
        }
    }
});

I need to pass one more parameter, CountryId. How can I do this?