using System;

using System.Collections.Generic;

using System.Linq;                  

public class Program

{

    public static void Main()

    {

        DateTime StartDate = DateTime.Now.AddDays(-14);

            DateTime EndDate = DateTime.Now;

            DayOfWeek day = DayOfWeek.Monday;

​

​

            List<DateTime> dates =

            Enumerable.Range(0, (int)((EndDate - StartDate).TotalDays) + 1)

                      .Select(n => StartDate.AddDays(n))

                      .ToList();

​

            var MondayCount = dates.Count(x => x.DayOfWeek == day);

            Console.WriteLine(day.ToString()+" occurs "+MondayCount+" times between "+StartDate.Date + " and "+EndDate.Date);

    }

}