In 1857, he left Cavendish due to poor health,[3] and spent three years traveling and studying in Minnesota and Philadelphia before taking up practice in Woburn, Massachusetts[4] in 1861.

Almost twenty years later, in 1868, he published a final paper recounting what he had been able to learn about the subsequent history of his patient (who died in 1860), and presenting psychological changes in Gage which, presumably, were sequelae of the accident.

[7] Harlow was highly active in Woburn civic affairs, serving at various times on the town's water, drainage, and schools committees, and as a library trustee; he was also a state senator and member of the Massachusetts Governor's Council, a trustee of the Massachusetts General Hospital, a bank president and director of another bank, a director of the local gas company, and a local medical official during the Civil War.

[1][8]: 195n18 On Harlow's death in 1907, The New York Times called him "one of the oldest and most prominent physicians and surgeons of New England".

[9] Childless (although twice married, first to Charlotte Davis and second to Frances Kimball), he left most of his substantial wealth to charity, for example endowing a ward for the poor at Massachusetts General Hospital and a book fund at Woburn Memorial High School's library, which is named for him.