As the River Boyne divides the dioceses of Armagh and Meath, Drogheda was founded as two separate towns, Drogheda-in-Meath (for which a charter was granted in 1194) and Drogheda-in-Oriel (or 'Uriel') as County Louth was then known. In 1412 these two towns were united and Drogheda became a 'County Corporate', styled as 'the County of the Town of Drogheda'. Drogheda continued as a County Borough until the setting up of County Councils, through the enactment of the Local Government (Ireland) Act 1898, which saw all of Drogheda, including a large area south of the Boyne, become part of an extended County Louth. With the passing of the County of Louth and Borough of Drogheda (Boundaries) Provisional Order, 1976, County Louth again grew larger at the expense of County Meath. The boundary was further altered in 1994 by the Local Government (Boundaries) (Town Elections) Regulations 1994. The 2007–2013 Meath County Development Plan recognises the Meath environs of Drogheda as a primary growth centre on a par with Navan.
In recent years Drogheda's economy has diversified from its traditional industries, with an increasing number of people employed in the retail, services and technology sectors. The town also has a community of independent artists and musicians who have been looking to the local economy rather than Dublin for employment.
The town is situated in an area with an abundance of archaeological monuments dating from the Neolithic period onwards, of which the large Passage Tombs of Newgrange, Knowth and Dowth are probably the best known. The remarkable density of archaeological sites of the prehistoric and Early Christian periods uncovered in recent years in the course of development, notably during construction of the Northern Motorway: Gormanston to Monasterboice, or 'Drogheda Bypass', have shown that the hinterland of Drogheda has been a settled landscape for millennia.
Despite local tradition linking Millmount to Amergin Glúingel, in his 1978 study of the history and archaeology of the town, John Bradley stated that "neither the documentary nor the archaeological evidence indicates that there was any settlement at the town prior to the coming of the Normans". The results of the numerous and often large-scale excavations carried out within the area of the medieval town in the past ten years appear to have confirmed this statement.
The earliest monument in the town is the motte-and-bailey castle, now known as Millmount Fort, which overlooks the town from a bluff on the south bank of the Boyne, and which was probably erected by the Norman Lord of Meath, Hugh de Lacy sometime before 1186. The earliest known town charter is that granted to Drogheda-in-Meath by Walter de lacy in 1194. In the 1600s the name of the town was also spelled "Tredagh" in keeping with the common pronunciation, as documented by Gerard Boate in his work Irelands' Natural History.
Drogheda was an important walled town in the English Pale in the medieval period. It frequently hosted meetings of the Irish Parliament at that time. In a spill-over from the War of the Roses, according to R.J.Mitchell in John Tiptoft, Earl of Worcester, the Earl of Desmond and his two youngest sons (still children) were executed there on Valentine's Day, 1468, on orders of the Earl of Worcester, the Lord Deputy of Ireland. It later came to light (see Robert Fabyan, "The New Chronicles of England and France"), that the Queen herself was implicated in the orders given. The parliament was moved to the town in 1494 and passed Poynings' Law, the most significant legislation in Irish history, a year later. This effectively subordinated the Irish Parliament's legislative powers to the King and his English Council.
The town was besieged twice during the Irish Confederate Wars. On the second occasion it was taken by Oliver Cromwell in September 1649, as part of the Cromwellian conquest of Ireland and it was the site of a massacre of the Royalist defenders. In his own words after the siege of Drogheda, "When they submitted, their officers were knocked on the head, and every tenth man of the soldiers killed and the rest shipped to Barbados."
In 1790 Drogheda Harbour Commissioners established, later Drogheda Port Company
In 1837 the population of Drogheda area was 17,365 of whom 15,138 lived in the town.
A Norman element on Drogheda's coat of arms is its centrepiece, St. Laurence's Gate. The three lions which flank the Norman barbican and the star and crescent, similar to those on the coat of arms of Portsmouth, are taken from Richard The Lionheart's coat of arms who gave both towns their charters. On the other side of the barbican is a ship denoting Drogheda's status as an important port. The town's motto Deus praesidium, mercatura decus translates as "God our strength, merchandise our glory".
A local narrative has it that the star and crescent were included in the town arms after the Ottoman Empire (predecessor to the Republic of Turkey) sent financial aid and ships laden with food to Drogheda during the Great Famine. There are no records of this with the Drogheda Port nor the Irish National Library, due to the fire that occurred in the 20th century. The star and crescent are thought to predate the famine. However, newspaper articles from the period refer to three foreign ships sailing up the River Boyne in May 1847. In addition, a letter found in Ottoman archives, written by Irish notables, explicitly thanks Sultan Abdülmecid I for his help.
A film is being shot regarding the subject as well.
In 1921 the preserved severed head of Saint Oliver Plunkett, who was executed in London in 1681, was put on display in St. Peter's Church, where it remains today. The church is located on West Street, which is the main street in the town.