Ayrshire is shaped like a crescent moon laid on its side, opening west towards the Firth of Clyde. To the north-east it borders the old counties of Renfrewshire and Lanarkshire; to the south-east, Dumfriesshire; to the south, Kirkcudbrightshire and Wigtownshire. The county is mostly flat with low hills, part of the Southern Uplands geographic region. The north holds most of the population - the main towns and the heaviest industry, historic and current. East of Largs rise the Renfrewshire Heights, running south to the hill country around Blae Loch. In the south, Ayrshire shares the rugged Galloway Hills with the Galloway counties: a tract of moor and rock west of the A713 that runs from Loch Doon almost down to the Solway Firth, with the Carsphairn and Scaur Hills further east and Glen Afton cutting deep into the country. Lying in the Firth itself are several small islands belonging to Ayrshire - Horse Isle, Lady Isle, and the granite plug of Ailsa Craig.

Long before the modern council areas, the shire of Ayr was divided into three districts or bailieries that survived for centuries. Carrick in the south sat between the River Doon and the wild Galloway country - hills and mosses for the most part. Kyle in the middle was the central district, containing the royal burgh of Ayr and running between the Irvine in the north and the Doon in the south. Kyle was further split into Kyle Stewart (or Stewart Kyle) between the Irvine and the Ayr, and King's Kyle, the triangle of land between the Ayr and the Doon - the country honoured as the birthplace and youthful home of Robert Burns. Cunninghame held the north. The names persist on signs and pub doors long after the bailiery system itself disappeared into history.

Ayrshire is one of the most agriculturally fertile regions in Scotland. Potatoes are grown in fields near the coast, fertilised with seaweed harvested from the same shore. The region produces pork, root vegetables, and beef - and summer berries, strawberries especially, grown abundantly enough that they once made the county famous. The breed of dairy cow named for the county - the Ayrshire, brown and white and known for its hardiness - became one of the standard dairy breeds of the English-speaking world. The Ayrshire countryside is a working landscape that still does what it has done for centuries, even as the rest of the economy has shifted to services, light industry, and (in the case of Prestwick) aerospace and aviation.

The territory was briefly occupied by the Romans during the reign of Emperor Antoninus Pius - the very edge of the Antonine Wall's southern reach. The local people, the Damnonii, were Britons. Later, the area was part of the Kingdom of Strathclyde, which was absorbed into the Kingdom of Scotland in the 11th century. In 1263, Scottish forces fought off a Norwegian leidang-army at the Battle of Largs - a skirmish more than a great battle, but the moment Norway's grip on the western seaboard began to slip. The county's most notable historic building is Turnberry Castle on the south Ayrshire coast, dating from the 13th century or earlier, and quite possibly the birthplace of Robert the Bruce.

When Ayrshire County Council was created in 1890, the burghs of Ayr and Kilmarnock were both deemed capable of running their own services and were excluded from county control. That changed in 1930 when the Local Government (Scotland) Act 1929 brought them back under the council and reclassified all burghs as large or small. Ayr and Kilmarnock kept large-burgh status; the county's other burghs ceded many functions to the county. In May 1975 the council was abolished altogether and replaced by Strathclyde Region with four districts inside it: Cumnock and Doon Valley, Cunninghame (including Arran and the Cumbraes, which had until then been part of Bute), Kilmarnock and Loudoun, and Kyle and Carrick. In 1996 those four districts became today's three council areas. The lieutenancy area is named Ayrshire and Arran. The boundaries of the old historic county still matter for some land registration purposes - a quiet survival of the geography that the bureaucracy keeps trying to redraw.

Railways link the northern towns to each other and to Glasgow, then south to Stranraer and south-east to Dumfries. Ferries connect Ayrshire to Arran and Great Cumbrae. Glasgow Prestwick International Airport sits 32 miles southwest of Glasgow itself - the "Glasgow" added to its name in American military airport convention, since the field served for decades as a stopover for US personnel moving between bases. Prestwick has one piece of cultural history nobody else can claim: it is the only place in Britain where Elvis Presley is known to have set foot, when his army transport home from West Germany refuelled there in 1960. He never came back.