you can use where condition as below, no need case statement
select U.NETWORKID, count(c.ID) as DEORECORDCOUNTDONE
from CUSTOMERLOANDATA C (nolock)
Inner Join USERMASTER U (nolock) on U.Id = C.CREATEDBY
where
(@Case=1 AND convert(varchar(10),c.createdon,120)= CONVERT(VARCHAR(10),'2014-02-28 12:48:57.000',120))
OR
(@Case=2 AND c.createdon <= '2014-06-01')
group by U.NETWORKID
order by U.NETWORKID