Kennett
Most likely a locational surname from a place-name, probably referring to someone who came from Kennet or a similar settlement.
The #9,245 most common surname in the United States (2010 Census) — about 1 in every 87,687 Americans shares it.
Etymology
Kennett is most likely a surname taken from a place-name. The historical sources you provided point to the family name being treated as local rather than descriptive, and one cited explanation links similar names to river-island or settlement forms. The underlying place-name may go back to Old English elements used for a habitation or geographical feature, but the exact derivation is not certain from these excerpts alone.
History
The name appears in medieval records and later remained in use as a family surname in England. The cited 19th-century writers treat it as a surname with local roots, though they do not give a single fully secure explanation for the exact place-name behind it. In modern usage it survives mainly as a relatively uncommon English surname.
Origin
Regions
Variant spellings
Fun fact
The name has been discussed by older surname scholars mainly as a local name, not as a nickname or occupation.
From the historical record
“weather, &c. ' Crotu, merry, brisk, lively ; crust or crtnts, saucy, mala- pert': Kennett, HS, Lansd. 1033. ' Axeyn bem wa^ he kene and cronH.' CorBorMund). (HalliweJl.)”
— A Dictionary of English and Welsh Surnames, with special American instances