I sometime get queries from people who have been tempted into genealogy by commercial websites such as Ancestry or FindMyPast and who appear never to have read a modern introductory guide to family history and haven't realised that commercial sites seem to go out of their way not to tell you of free web sites which contain answers to the question you are asking, such as familysearch.
As a result I have now updated my page on FreeBMD and included details of the related sites FreeCEN and FreeREG.
FreeBMG contains complete indexes of birth, marriage and death registrations from July 1837 to 1939 for births, 1951 for marriages, and 1950 for deaths. Some later years are fully indexed and the coverage is steadily being increased.
FreeCEN contains census returns and as yet coverage for Hertfordshire is limited to 1851 (25% coverage), 1871 (9.5% coverage) and 1891 (8.3% coverage).
FreeREG contains indexed parish and non-conformist records and the coverage for Hertfordshire is currently limited - but may include the parish you are interested in.
If you have some free time why not volunteer to be an indexer of Hertfordshire registers or censuses for FreeREG or FreeCEN. Not only will you find this interesting but you will also be helping your fellow genealogists.