On 7 January 1849, Dickens visited Norwich and Yarmouth in Norfolk, with two close friends, John Leech (1817–1864) and Mark Lemon (1809–1870). Leech was an illustrator at Punch, a satirical magazine, and the first illustrator for A Christmas Carol by Dickens in 1843. Lemon was a founding editor of Punch, and soon a contributor to Household Words, the weekly magazine Dickens was starting up; he co-authored Mr Nightingale's Diary, a farce, with Dickens in 1851. The two towns, especially the second, became important in the novel, and Dickens informed Forster that Yarmouth seemed to him to be "the strangest place in the world" and that he would "certainly try my hand at it". During a walk in the vicinity of Yarmouth, Dickens noticed a sign indicating the small locality of Blunderston, which became in his novel the village of "Blunderstone" where David is born and spends his childhood.
A week after Charles's arrival in Yarmouth, his sixth son, Henry Fielding Dickens, was named after Henry Fielding, his favorite past author. Per Forster, Dickens refers to Fielding "as a kind of homage to the novel he was about to write".
Changes in detail occur during the composition: on 22 August 1849, while staying on the Isle of Wight for a family vacation, he changed on the advice of Forster, the theme of the obsession of Mr Dick, a secondary character in the novel. This theme was originally "a bull in a china shop" and became "King Charles's head" in a nod to the bicentenary of the execution of Charles I of England.
On 4 November 1849, when Blackwell was treating an infant with ophthalmia neonatorum, she spurted some contaminated solution into her own eye accidentally and contracted the infection. She lost sight in her left eye, causing her to have her eye surgically extracted and thus lost all hope of becoming a surgeon.