You would definitely need to order the birth cert, unless I have found the wrong people...but Hilsden isn't that common a name in Essex at the time.
Because I have found a marriage between a William HILSDEN and an Elizabeth SMITH in 1872 (which was the year that George William was registered) Marriage: 1872 OND Halstead 4a/665
According the 1881 census, William Hilsden was born in 1852 in Toppesfield, Essex
1871 census: William HILSDEN b. 1852 Toppesfield Aged 19, parents Isaac and Mary Ann
However in the 1881 census, George William was not the eldest son, there was a son, Harry who was 3 years older than him...cannot find birth reg for him at present!
Added: In the 1891 census, there is a James H Hilsden who is 3 years older than George William. I'm figuring this is Harry. There is no birth reg for a Harry Hilsden, James H Hilsden or a James Hilsden for 3 years before George's birth (Ie. 1869) however there is a James SMITH b. 1869 JAS HAlstead 4a/337