using System;

using System.Linq;

using System.Collections.Generic;

using Newtonsoft.Json;

public class Program

{

    public static void Main()

    {

        string input = @"{

    ""Status"": ""OK"",

    ""ResultInfo"": {

        ""Prev"": ""PageUPURL"",

        ""Next"": ""PageDownURL"",

        ""total_count"": ""37"",

        ""per_page"": ""3"",

        ""page"": ""1""

    },

    ""Message"": ""Ok."",

    ""Data"": {

        ""Item1"": [

            {

                ""SubItem1"": [

                    ""Text FOO""

                ]

            }

        ],

        ""Item2"": [

            {

                ""SubItem2"": [

                    ""Text"",

                    ""Text"",

                    ""Text""

                ]

            }

        ],

        ""Item3"": [

            {

                ""SubItem3"": [

                    ""Text""

                ]

            },

            {

                ""SubItem4"": [

                    ""Text""

                ]

            }

        ]

    }

}";

        var resultS = JsonConvert.DeserializeObject<RootSelf>(input);       

        resultS.Data.Dump();        

        resultS.Data["Item1"].Dump();

        resultS.Data["Item1"].First()["SubItem1"].Dump();

    }

    public class RootSelf

    {

        public string Status { get; set; }

        public ResultInfo ResultInfo { get; set; }

        public string Message { get; set; }

        public Dictionary<string, List<Dictionary<string, List<string>>>> Data { get; set; }

    }   

    public partial class ResultInfo

    {

        [JsonProperty("Prev")]

        public string Prev { get; set; }

​

        [JsonProperty("Next")]

        public string Next { get; set; }

​

        [JsonProperty("total_count")]

        public int TotalCount { get; set; }

​

        [JsonProperty("per_page")]

        public int PerPage { get; set; }

​

        [JsonProperty("page")]

        public int Page { get; set; }

    }

}