Denning
A surname with multiple possible roots, most likely a patronymic or nickname form built from the old personal name Denn/Dan or related diminutive forms.
The #4,402 most common surname in the United States (2010 Census) — about 1 in every 38,230 Americans shares it.
Etymology
The surname Denning is best understood as a family-name form built from a shorter personal name such as Denn, Dan, or a related pet form. The historical dictionaries you provided connect it with old German and English name forms like Daning/Dening, while Irish material also places it among surnames that can overlap with Gaelic names rendered in English spelling. In other words, the literal sense is not certain, but it likely began as 'descendant of' or 'belonging to' someone called Denn/Dan rather than from an occupation or place.
History
The name appears in English and Irish surname lists in the 19th and early 20th centuries, which suggests parallel or overlapping origins rather than a single family line. Some older onomastic works group Denning with forms such as Denny, Dennison, and Denson, pointing to a broader cluster of surnames derived from short personal names. In Ireland, it may sometimes reflect anglicized Gaelic surnames or a separate local development, so the spelling can conceal different family histories.
Origin
Regions
Variant spellings
Fun fact
The form Denning was already being discussed alongside similar surnames in 19th-century name dictionaries, showing how many modern spellings grew out of a small set of medieval nickname forms.
From the historical record
“452 DENNING. DiiHly' Dinnegan. 3. 493 DORAN. Dening.”
— Varieties and Synonymes of Surnames and Christian Names in Ireland