You can keep your existing ActionMethod untouched without the need of json serializing:
In the client side create an object from your json:
JSON.parse(jsonData)
and send that in the $.ajax data property.
Or, instead of creating json, create an object:
var dataObject = new Object();
dataObject.Town = $('#txt-Town').val();
dataObject.District = $('#txt-District').val();
...
And again, send that object in the $.ajax data property.