James Duffy b.1882 emigrated to England- Prescot by 1911

Do you have his fathers' name & occupation from his marriage cert ?

Having this information could help narrow down, or rule out, possible birth records. Ages are not always accurate so it's best to allow at least a few years either way when searching.  Other details that may help are the witnesses to the marriages that could be related or godparents to his children, also worth checking for relations either in the same household or nearby on the English census returns to see if any give a more detailed place of birth. The usual process is checking all applicable England/Wales census returns, but if your James only arrived c1909 then the only two options are 1911 and 1921 census

Another English source worth checking if your James was still in England at the time, is the 1939 register - this records date of birth .. might not be 100% accurate but worth checking

Birth records are available on the free IrishGenealogy website form the start of registration in 1864 up to about 1920
 

for reference - probable 1911 census info. for James :
Address : 19 Sandon Street St Helens, St Helens, Lancashire
James Duffy age 29 stone-miner in coal mine, pob Co. Galway

Wife Maria age 31 born Stoke, Staffordshire - couple report they are married 5 years so c1906

3 children up to age 5 all born St. Helen's Lancs.

also in the household 2 nephews and a niece - all Duffy

Given Maria's place of birth I'd suggest a marriage in England is most likely - either Staffordshire or Lancashire

Youngest child of James & Maria is Mary Rita age one month, a search on the England/Wales BMD Index shows a promising match for her as Mary R. Duffy born 2nd quarter 1911 in Prescot registration district - same district as that 1911 census, mother's maiden surname is Jones - does this sound correct for your Duffy family ?
 

just checked for likely births of the other children shown on the 1911 census - and located a very promising index match for the niece Honor Duffy age 8, registered 1st quarter 1903 in Prescot district, mother's maiden surname is Jones -  so looks like a brother to your James may have married a sister of Maria...

one more for now - believe I've located your James with his brothers Thomas & Peter on the 1901 census - all coal miners born Ireland.

Thomas Duffy is married to a Maria born Stoke, Staffs. and they have 2 children James & John, also in the same household are two lodgers, surname Connelly also from Ireland.

Address for this return is 21, Prescott Street, St Helens, Prescot, Lancashire

Wow, this is amazingly helpful, thank you so much!! Ok so I have much more to go on now, that should keep me busy for a while :) thanks again!