The historic Kingdom of Mide was one of the great political units of medieval Ireland, ruled by the southern Ui Neill from royal sites including the Hill of Tara (just over the border in modern Meath) and Lough Ennell. Mael Sechnaill II - a Westmeath native - was both King of Mide and High King of Ireland, and was the man who defeated Brian Boru's son and recovered the high-kingship after the Battle of Clontarf in 1014. The Norman Walter de Lacy was granted the Lordship of Meath after the Norman invasion, and his descendants and tenants built the great Norman castles that still dot the county. In 1543 the Parliament of Ireland passed the Counties of Meath and Westmeath Act, splitting the old administrative county of Meath into eastern Meath and western Westmeath. The big Anglo-Irish family of the modern county was the Pakenhams, the Earls of Longford, whose seat at Pakenham Hall (now Tullynally Castle) is one of the largest castles in Ireland; from the Pakenhams came Field Marshal Edward Pakenham, killed leading the British attack at the Battle of New Orleans in 1815, and his much more peaceful descendant Thomas Pakenham, the historian and arborist whose photographs of ancient trees are world-famous.

Westmeath is a lake county. Lough Derravaragh in the north - long, narrow, and ringed with reed beds - is the traditional setting of the great Irish legend of the Children of Lir, who were turned into swans by their stepmother and spent three hundred years on its waters. Lough Ennell, just south of Mullingar, was the seat of the medieval Ui Neill high-kings of Mide. Lough Owel feeds Mullingar's water supply. Lough Lene to the east has unusually clear water and its own freshwater jellyfish. Lough Sheelin straddles the border with Cavan. And Lough Ree, the second-largest lake on the Shannon, forms the long western boundary of the county. The Royal Canal, opened in the early nineteenth century to link Dublin to the Shannon at Cloondara, runs through Mullingar and shaped its commercial growth - the canal made it cheap to ship Westmeath beef, cheese, and grain to Dublin and onward to England. The whole canal is now a 130-kilometre walking and cycling greenway. The Athlone-to-Mullingar section of the old Midland Great Western Railway, abandoned in the 1980s, was reopened as a greenway in 2015 and links into the Royal Canal route, giving the county over 100 km of off-road cycling.

Industry in Westmeath has long centred on three things: cattle, whiskey, and horses. The plains around Mullingar are famous for the quality of their beef and veal - young cattle weaned in the west of Ireland are brought across the Shannon and fattened for market on the calcium-rich grasslands here. Kilbeggan, in the south of the county, has held a whiskey distillery since 1757 - making Kilbeggan Distillery the oldest licensed whiskey distillery in the world. It closed in 1957 and was reopened in 2007 by the Cooley Distillery as a working museum and craft producer. And the limestone-rich marl soils of central Westmeath are unusually good for raising horses - the calcium passes from the grass into the developing bones of foals, making the county one of Ireland's most important centres for thoroughbred breeding. Cecil Boyd-Rochfort, the Westmeath-born British royal trainer, trained Queen Elizabeth II's horses and was knighted for it. More recently, Athlone is associated with many of Ireland's most prominent companies, and Michael O'Leary - the chief executive of Ryanair, whose headquarters are at Airside Business Park near Dublin Airport - is from Mullingar.

Westmeath has a distinctive showband and pop music heritage. Joe Dolan, born in Mullingar in 1939, was one of the biggest Irish pop stars of his generation - 'Make Me an Island' reached number three in the UK chart in 1969 - and he kept performing in Mullingar until shortly before his death in 2007. The county has produced the dance-band singer Brendan Shine, the country singer Ray Lynam, the showband duo Foster and Allen, and the indie band The Academic. The biggest pop export, though, is Niall Horan - born in Mullingar in 1993, where his Joe Dolan childhood would not have been possible without Westmeath's previous generation - who auditioned for The X Factor in 2010, was put together with four other young men into the band One Direction, and went on to have one of the most successful pop careers of the twenty-first century. The Irish-language singer Emmet Cahill of Celtic Thunder is from Mullingar. So is Robbie Henshaw, the Irish rugby international. The county is also home to the Christ the King Cathedral in Mullingar, the largest cathedral in Ireland of twentieth-century construction, finished in 1936 with two great pinnacle towers visible across the surrounding plain.