Topographic surname for someone living near a marsh or wetland, from Old English 'mersc'.
Marsh descends from the Old English mærsc, a straightforward topographic word for the wetland ecosystems that once defined so much of the British lowland landscape. As a surname it identified families who lived near or worked within marshes — the reed-cutters, wildfowlers, and fen farmers whose livelihoods were inseparable from those watery borderlands. Like many English nature-surnames, it made the occasional leap to given-name use, particularly in regions where such terrain was locally distinctive, and it carries that earthy, uncomposed quality of landscape names.
As a given name Marsh sits in rare, quietly distinctive company. The most famous bearer is probably Ngaio Marsh, the New Zealand crime writer whose elegant detective fiction placed her alongside Agatha Christie and Dorothy L. Sayers in the "Golden Age" pantheon — though Ngaio was her first name and Marsh her surname.
In American usage, Marsh has appeared as a masculine first name in families honoring a family surname, a pattern common in nineteenth and early twentieth century naming traditions when preserving maternal maiden names was a matter of genealogical pride. Today Marsh occupies the same terrain as other monosyllabic English nature surnames — Reed, Grove, Heath, Fen — that periodically attract parents seeking something grounded and unadorned. It carries the smell of morning mist and open country, a name that does not announce itself loudly but settles quietly into memory. Its rarity is itself a kind of recommendation: a child named Marsh will almost never share the name with a classmate, yet it requires no explanation.