The surname Hessom appears to be associated with the Lancashire village of Heysham on Morecambe Bay. The residents of Heysham pronounce the name of their village HEE-SHAM (not HAY-SHAM) and have done so, it is said, for at least 150 years. The village pre-dates the Norman conquest and gets a mention in the Domesday book. One of several proposed etymologies has it derived from HESSE-HAM, i.e. the home of Hesse, presumably a Saxon chieftain.
I like the etymology HESSE-HAM, because it's easy to imagine how this could have come to be pronounced HEES-HAM, with a long E, a sibilant S, an H which is easily dropped (or not noticed), and the stress on the first syllable. It is likely that the surname was pronounced something like this in Cheshire around 1800, because we find families in the records whose names were spelled in all of these ways: HEESHAM, HEASHAM, HEESOM, HESOM, HESSOM, and HISSOM. Earlier variations include HEYSAM and HEYSUM.Today, we tend to take for granted the idea that a surname has a correct spelling. Many Hessoms would resist the suggestion that they were close cousins to the Heesoms in the next parish (and vice versa). Yet this idea is quite recent. At the start of the 19th century, literacy in England was not the rule but the exception. By the end of the century, the situation had reversed. Families learned the correct spelling of their surname from their vicar or schoolmaster, and passed it on to their own children; the common people gradually became the authorities on the spelling of their own names. The chance divergence of spelling of the surnames of two brothers in the same parish's register of baptisms became the dogma of their children, and the kinship of their descendants was soon forgotten.
If you're researching Hessoms, even as late as the nineteenth century, you need to be alert for a host of genuine variations:
HESSOM, HESSOME, HESOM, HEESOM, HEESHAM, HEASHAM, HISSOM, HISSEM, HEYSHAM, HEYSAM, HEYSUM, etc.as well as common transcription errors, such as HUSSOM (a handwritten EE sometimes looks very like a U), or HERSOM. Also watch out for HESSON or HEESON, which can arise either as a later transcription error or as the best attempt of the vicar, enumerator or clerk to write down the name that they thought they heard; I've seen several documents where the clerk has written HESSON but the person has signed HESSOM.