Ballincollig Castle is a Norman castle to the south of the town of Ballincollig, County Cork, Ireland, built after the Norman invasion of Ireland. In its prime, the castle was inhabited by the Barrett family, who had control of the local area. The castle still stands today, albeit largely in ruin. The original keep still remains, as does most of the curtain wall and two towers.

An earlier castle may have been built on the site by Sir Robert Coll, a Norman knight, whose name also likely influenced the name of the town of Ballincollig (Baile an Choillaigh or the 'Town of the Colls'). While a date for this original construction is not confirmed, by 1468, the Barrett family purchased Coll's estate lands at Ballincollig, and improved and extended the castle site. The main structures of Ballincollig Castle were constructed at this time.

The bawn (enclosure) and tower house are located on a limestone summit, which has a line of sight over the low land of the Maglin Valley. Beneath the castle there is a natural cavern which runs into the rock, and around it the remains of a moat.

Members of the Barrett family had travelled from Normandy with William the Conqueror. Some of these Barretts travelled with the Normans to Ireland in 1169. When Henry II parceled out the spoils of conquest in Ireland, he gave the Kingdom of Cork (from Lismore, County Waterford to County Kerry) to Milo de Cogan. De Cogan (Goggin) received land west and south of the city, and the family built a number of castles on their lands. The Barretts were underlords of the de Cogans, and travelled to conquer Connacht in 1235 under John de Cogan. They, under John Barrett, subsequently become tenants of the de Cogans at Carrigrohane. By the 15th century, the Barretts were underlords of the MacCarthys, to whom they paid rent of £11 a year from 1420. They were later tenants of the Earls of Desmond, to whom they paid 12 marks yearly. By the late 1460s, the Barretts purchased Ballincollig Castle outright. This is recorded in the Carew Calendar of 28 November 1611, with Sir Dominic Sarsfield writing to Lord Carew: "Ballincollig is entailed and was purchased in the 8th year of Edward 4 (1468–9) from Robert Coil [Coll], a knight. Deed of entail in my own lands".

The castle became the principal Barrett stronghold until the early 17th century, when the Castlemore Barretts seem to have had control over Mourne Abbey and Garrycloyne (both in the north of the Barony), together with Castleinch, Ballincollig and Cloghan McUllick. The Barretts also controlled Carrigrohane for some time.

During the 1590s, a dispute arose. In July 1591, Andrew Barrett and sixty others assaulted Ballincollig Castle and dispossessed Edmund Barrett, "with swords, guns, great sledges or hammers, skenes, stones and staves". Three years later, Edmund got a decree of £100 against the Sheriff of County Cork, for refusing to execute a writ dispossessing Andrew Barrett and others who had seized the castle. In the following year, 1595, Edmund took his cousin to court. A fine of £20 was imposed on Andrew and lesser fines on two others, and they were jailed.

By the early 17th century, the Barretts had lost Ballincollig Castle. The family had borrowed money to pay for court fines and dowries, and obtained a mortgage on the castle and lands in 1618 from the Coppingers of Cork. Contemporary papers note that "William Barrett of Ballincollig in the County of Cork, gent,… in consideration of £240 paid by Edmond Coppinger Fitzrobert of Corke, gent, the said William Barrett granted to the said Edmond Coppinger, his heirs and assigns forever all that and those the castles, bawnes, towns, villages, hamlets, lands, tenements and hereditaments of and in Ballincolly…". This mortgage was transferred to Sir Walter Coppinger, Cloghane (near Skibbereen) and in 1630 for the payment of £790 to the Barretts, Coppinger came into full possession of the castle and lands.

By 1644, the castle was taken by Oliver Cromwell's forces, and around 1689 it was garrisoned for James II. After 1690, it fell into disuse and disrepair.