The action takes place in the imaginary town of Trumpton, a short distance from the equally imaginary town of Camberwick Green, the focus of the first series in the Trumptonshire Trilogy. Each episode begins with a shot of Trumpton Town Hall Clock: "Telling the time, steadily, sensibly; never too quickly, never too slowly. Telling the time for Trumpton". The townsfolk then appear going about their daily business: the Mayor, Mr Troop the Town Clerk, Chippy Minton the carpenter and his apprentice son Nibbs, Mrs Cobbit the florist, Miss Lovelace the milliner and her trio of pekingese dogs (Mitzi, Daphne and Lulu), and Mr Platt the clockmaker.
Although all of the characters and settings are new, the style of the programme follows the pattern established by Camberwick Green, in which domestic problems are cheerfully resolved by the end of the show, leaving the last minute or so for the Fire Brigade to become the Fire Brigade Band and play the episode out.
The Fire Brigade is perhaps Trumpton's most-recognised feature. Captain Flack's roll-call was recited in all but one episode: "Pugh, Pugh, Barney McGrew, Cuthbert, Dibble, Grub." Puppeteer Gordon Murray explains that "Pugh and Pugh are twins you must understand - not Hugh, Pugh." In the episode "Cuthbert's Morning Off", Cuthbert's name is omitted. They are continually being called out to attend some emergency or other (in many cases to resolve fairly trivial matters), but to Captain Flack's annoyance never an actual fire. The main reason for this was the impossibility of animating fire, water and smoke. However, after "Right men, action stations!", this doesn't stop the Fire Brigade absent-mindedly getting out the fire hose and receiving a rebuke from Captain Flack ("No no! Not the hose!").
Gordon Murray has consistently denied that the names of the places in the series were based on any real villages, however it has often been assumed that they are derived from names within East Sussex: Camberwick Green from Wivelsfield Green, Trumpton from Plumpton and Chigley from Chailey.