I got the Answer :
var data5 = (from SF in VDC.SURVEY_FOLDER
join ST in VDC.SURVEY_TEMPLATE on new { FOLDER_ID = SF.FOLDER_ID } equals new { FOLDER_ID = (Int64)ST.FOLDER_ID } into ST_join
from ST in ST_join.DefaultIfEmpty()
group new { SF, ST } by new
{
SF.FOLDER_NAME,
SF.CREATED_DATE
} into g
select new
{
g.Key.FOLDER_NAME,
CREATED_DATE = (DateTime?)g.Key.CREATED_DATE,
Column1 = (Int64?)g.Count(p => p.ST.FOLDER_ID != null)
}).ToList();