Ballymena (/ˌbæliˈmiːnə/ BAL-ee-MEE-nə; from Irish: an Baile Meánach [ənˠ ˌbˠalʲə ˈmʲaːn̪ˠəx]^ⓘ, meaning 'the middle townland') is a town in County Antrim, Northern Ireland. It had a population of 31,205 people at the 2021 United Kingdom census, making it the seventh largest town in Northern Ireland by population. It is part of the Borough of Mid and East Antrim.

The town was built on the Braid River, on land given to the Adair family by King Charles I in 1626, with a right to hold two annual fairs and a Saturday market in perpetuity. Surrounding villages are Cullybackey, Ahoghill, Broughshane, and Kells-Connor.

The recorded history of the Ballymena area dates to the Early Christian period, from the fifth to the seventh centuries. Ringforts are found in the townland of Ballykeel, and a site known as Camphill Fort in the townland of Ballee may also have been of this type. There are a number of souterrains within a 1+1⁄4 miles (2.0 km) radius of the centre of Ballymena. Two miles (3.2 kilometres) north in the townland of Kirkinriola, the medieval parish church and graveyard show signs of Early Christian settlement, including a souterrain. Also in 1868, a gravedigger found a large stone slab on which was carved a cross with the inscription ord do degen. This refers to Bishop Degen, who lived in Ireland during the seventh century. This stone is now in the porch of St Patrick's Church of Ireland, at the end of Castle Street. At the end of the fifth century, a church was founded in Connor, five miles (8.0 kilometres) south of Ballymena. This was followed by a monastery at Templemoyle, Kells. In 831, Vikings invaded the area and burned the church.

In the late 12th century, the Anglo-Normans invaded Ireland and conquered much of what is now eastern Ulster, creating the Earldom of Ulster. They built a motte-and-bailey fort in what is now the Harryville area of Ballymena. It is one of the best-surviving examples of this type of fortification in Northern Ireland.

In 1315, Edward Bruce (brother of Scottish king Robert the Bruce) invaded the Earldom of Ulster, opening up another front in the war against the English. On 10 September 1315, at the Battle of Connor, near Ballymena, Edward's army defeated the army of Richard de Burgh, the Anglo-Norman Earl of Ulster.

On 10 May 1607, during the Plantation of Ulster, King James I of England granted the native Irish chief, Ruairí Óg MacQuillan, the Ballymena Estate. The estate passed through several owners, eventually passing into the possession of William Adair, a Scottish laird from Kinhilt in southwestern Scotland. The estate was temporarily renamed "Kinhilstown" after Adair's lands in Scotland. The original castle of Ballymena was built in the early 17th century, situated to take advantage of an ancient ford on the River Braid. In 1626 Charles I confirmed the grant of the Ballymena Estate to William Adair, giving him the right to hold a market at Ballymena every Saturday. He hired local Irish as workers on the estate; they served as tenant farmers for much of the next two centuries and more. Galgorm nearby was granted to Sir Faithful Fortescue. In 1618 he built the Castle, which still exists.

During the Irish Rebellion of 1641, the local Ballymena garrison were defeated by Irish rebels in the battle of Bundooragh.

Ballymena's first market hall was built in 1684.