The townland and farm at Ballygar - historically Beallagarr - are recorded as far back as 1585. That August, the chieftains and landowners of Galway and Roscommon were summoned to Galway city to meet the Lord Deputy, Sir John Perrot. They were to surrender their lands to Elizabeth I and receive them back as Crown leases at a penny an acre. The terms were accepted - the alternative was war - and one of the signatories was Francis Shane of Ballygar, possibly the proprietor of the local castle. By the 1640s the castle held a garrison. By the early 18th century it had disappeared from the records. By 1820 there was nothing here but pasture and the River Suck, until Denis Henry Kelly decided to build a town.

Kelly planned Ballygar with the precision of an engineer: a wide main street, a market square, a diamond at the entrance to his Castle Kelly estate, two back streets for rear access to every premises. He built the shops and houses himself and let them to tenants he selected carefully. The market that opened in 1820 worked: by 1840 it traded more than anywhere in Connacht except Athlone. Twenty years after foundation Ballygar had 52 houses and 363 residents, plus 5,300 on the broader Kelly estate per the 1841 census. The cleanliness contest was eccentric but effective. The Reproductive Loan Fund, introduced in 1835, was something closer to revolutionary - a credit union before credit unions existed, lending to tenants in hard times, with £1,000 circulating locally by 1844.

The Great Famine - An Gorta Mor - hit Ballygar like every part of rural Connacht. Between 1845 and 1849 the potato failed, and the failure killed people the local landlords kept demanding rent from. Few firsthand accounts survive. The history was too painful, the local people too ashamed of what poverty had forced families to do: selling eggs and animals to make rent while their neighbours starved beside them. In a field in Ballinacor village, five simple graves lie next to a sandpit - one with field stones around it. They are almost certainly Famine victims, buried without ceremony and likely without a priest. Norma Hoilean's research on Trihill National School records how the entire townland of Bohill emigrated on the same day, the whole community taking their meagre belongings to the coffin ships at Cobh or Galway. No one knows what became of them.

In 1863 the Kelly estate went on the market under the Encumbered Estates Act - 12,000 acres including the castle and town, bought by Christopher Neville Bagott for £105,000. The Bagott family ran the estate at arm's length. Christopher kept a London house and threw lavish parties, at one of which he met Alice Verner, a young woman of charm and beauty. They married around 1874. Their relations soured quickly. He banished her and their young son from Castle Kelly, drew up a will leaving everything to his brother John, and died in May 1877 with his health collapsed. Alice contested the will. The Probate Court in Dublin heard the case for a month and found for the widow and her son. The estate was administered for them until the heir came of age. In 1903 it was sold to the Land Commission, and later the Forestry Commission took Castlekelly and the 1,600 acres around it.

Ballygar's most famous son left as a young man, emigrated to America, joined the Union Army, and became the leading bandmaster of the United States. Patrick Sarsfield Gilmore was born here in 1829. By the 1860s he was bandleader for the 24th Massachusetts Regiment, then for General Banks's Army of the Gulf in Louisiana. In 1863, in New Orleans, he wrote 'When Johnny Comes Marching Home' - a song that swept the Civil War, was sung by both Union and Confederate soldiers, and has stayed in the American songbook ever since. Mattie McDonagh, born in the parish a century later, won four All-Ireland Senior Football medals for Galway - the only Connacht man ever to do so. In 2003 Ballygar welcomed the Afghanistan Special Olympics team. The carnival has run every year since 1945. Murray Timber Products, founded in 1977, is now one of Ireland's largest sawmills. The town that Denis Kelly built is still here, though most of his cleanliness tickets are long gone.