select  Owner AS PropOwner, count(Owner) AS CountOfProp from tblProp Group by Owner 

 using (con = new SqlConnection(cs))
            {
                cmd = new SqlCommand("select  Owner AS PropOwner, count(Owner) AS CountOfProp from tblProp Group by Owner ",con)
                Series series = Chart1.Series["Series1"];
                con.Open();
                using (SqlDataReader reader = cmd.ExecuteReader())
                {
                    while(reader.Read())
                    {
                        series.Points.AddXY(reader["PropOwner"].ToString(), reader["CountOfProp"]);
                    }
                }
            }