How County Down and County Londonderry Got Their Names

There is no "Co Down" in Ireland — but there are two Northern Irish counties with similar names: County Down and County Londonderry (often called "Derry"). Here's the etymology of each.

County Down (An Dún)

Origin 1: Dún = Fort / Stronghold

• Old Irish dún "fort, fortified place" (cognate with English "town", "dune")
• Refers to the numerous ancient hillforts (ráths, dúns) dotting the drumlin landscape
• Key sites: Downpatrick (Dún Pádraig — Patrick's fort), Dundrum (Dún Droma — ridge fort)

Origin 2: Dubh = Black / Dark

• Alternative: dubh "black" → dark, fertile soils of the Lecale plain
• Supported by early spellings: Dun, Doune, Doun

Consensus: Dún (fort) is primary — the drumlin belt has 1,000+ raths.

County Londonderry / Derry (Doire)

Original Irish: Doire Cholm Cille

• Doire = "oak grove / oak wood"
• Cholm Cille = "of Colm Cille" (St. Columba / Colmcille, 6th c. missionary)
• Meaning: "Oak Wood of Colm Cille" — the monastery he founded (546 CE)

Anglicization Path

1. Doire → Derry (phonetic)
2. 1613: London guilds funded plantation → "London" prefix added → Londonderry
3. Contested: Nationalists use Derry; Unionists use Londonderry; official = Londonderry

Why "Co Down" Doesn't Exist

• "Co." = abbreviation for "County" — used in addresses: "Co. Down"
• But no county named "Co Down" — it's County Down
• "Co Derry" is similarly informal for County Londonderry

Quick Comparison

Two counties. Two ancient roots. One letter apart in abbreviation. Now you know the difference.