C# Deserialize deep linked object

I have the following JSON data:

{
    "count": 2,

    "data" : {
        "items" : [
            {
                "id" : "1",
                "letterheadline" : "This is a test",
                "message" : "testing.. testing..",
                "dateEntered" : "2018-01-01 18:00"
            },

            {
                "id" : "2",
                "letterheadline" : "Message two",
                "message" : "testing.. testing.. testing..",
                "dateEntered" : "2018-02-01 18:00"
            },


        ]
    }

}

I am trying to parse it into my own object that uses different values, i.e:

public class Message 
{
    public string title {get; set;}

    public string body {get; set;}

    public DateTime entryDate {get; set;}
}

public class Messages
{
    public int itemCount {get; set;}

    public List<Message> messages {get; set}
}

I am using

Messages messages = new JavaScriptSerializer().Deserialize<Messages>(result);

I have tried to use the following:

[JsonProperty("letterheadline")] (for example)

But I am still getting an error saying that it cannot be converted.

Is this because the JSON data itself is too deep to parse? Therefore would I need to create a new property Data inside my object that contains a list of Messages?