Willoughby is the kind of name that arrives in a waistcoat. It's deeply English, deeply literary, and sufficiently pompous-sounding that placing it on a dog creates an instant character — one who regards you with mild disappointment and expects his dinner to be served on time. The name has never been common in the US, which makes it feel entirely invented even when it isn't.
Austen Country
John Willoughby is the charismatic, ultimately disappointing love interest in Jane Austen's Sense and Sensibility — handsome, charming, and morally unreliable. Naming a dog Willoughby after this character is a specific literary joke that rewards the people who catch it. The name works equally well for owners who simply want something English-sounding without the literary reference. English Springer Spaniels and Cavalier King Charles Spaniels are natural fits.
The Long-Name Appeal
Four syllables is a commitment in a pet name, but Willoughby earns it by having a built-in nickname (Will, Wills, Wigby) that owners can land on after the formality wears in. The long-form name stays on the registration; the daily name evolves naturally. Compare with Pemberton and Fitzwilliam for similar English-estate energy.
Counter-Reading: Commitment Check
Four-syllable names require genuine enthusiasm to sustain. If you're not fully in love with Willoughby on day one, the fatigue arrives by week three. Test it aloud at the dog park before committing — "Willoughby, come!" is a sentence that requires confidence to deliver without irony.