[8] In 868 King Alfred married Ealhswith (Ealswitha), daughter of Æthelred Mucel, chief of the Gaini, whence the town gets its name.

Towards the end of July 1013, the Dane Sweyn Forkbeard and his son and heir Cnut (Canute) arrived in Gainsborough with an army of conquest.

The Domesday Book (1086) records that Gainsborough was a community of farmers, villeins and sokemen, tenants of Geoffrey de Guerche.

Parliament captured Gainsborough in the battle on 20 July, but it was immediately besieged by a large Royalist army and forced to surrender after three days.

Parliament captured Gainsborough again on 18 December 1643, but had to withdraw in March 1644, razing the town's defences to prevent their use by the enemy.

[13] The first record of a church at Gainsborough is in 1180, when the rectory there was granted by Roger de Talebu to the great Preceptory of the Knights Templar in Lindsey, at Willoughton.

In 1736 it was demolished to make way for a new parish church completed in 1748 in a mix of perpendicular Gothic and Classical Revival styles.

A monument to Richard Rollett, master sailmaker on Captain James Cook's second voyage, is located in the porch.

It has often been claimed that some of the Mayflower Pilgrims worshipped in secret at the Old Hall before sailing for Holland to find religious freedom in 1609; no historical evidence for this has been found, whereas the congregation of John Smyth that met in the town developed into the Baptists and some returned to England.

[15] Now the United Reformed Church, it was named in honour of John Robinson (1576–1625), pastor of the "Pilgrim Fathers" before they left on the Mayflower.

The town's first Methodist chapel opened in Church Lane in 1788, moving to a new site in North Street in 1804, and rebuilt there as St Stephen's in 1966.

The Primitive Methodists set up in the town in 1819, with chapels in Spring Gardens (1838), Trinity Street (1877) and Ropery Road (1910).

On the night of 28–29 April 1942 a single Dornier 217 dropped a stick of bombs on the town centre, causing extensive damage and the loss of seven lives.

On 31 December 1942, a RCAF Bristol Beaufighter aircraft on a training exercise crashed on Noel Street, killing both airmen and a three-year-old girl.

In the early hours of 5 March 1945 a single Junkers Ju 88 fighter/bomber made a low-level attack over the town, dropping anti-personnel bombs on Church Street and the surrounding residential area.

In order to see Mr and Mrs Glegg at home, we must enter the town of St Ogg's, — that venerable town with the red fluted roofs and the broad warehouse gables, where the black ships unlade themselves of their burthens from the far north, and carry away, in exchange, the precious inland products, the well-crushed cheese and the soft fleeces which my refined readers have doubtless become acquainted with through the medium of the best classic pastorals.

It is one of those old, old towns which impress one as a continuation and outgrowth of nature, as much as the nests of the bower-birds or the winding galleries of the white ants; a town which carries the traces of its long growth and history like a millennial tree, and has sprung up and developed in the same spot between the river and the low hill from the time when the Roman legions turned their backs on it from the camp on the hillside, and the long-haired sea-kings came up the river and looked with fierce, eager eyes at the fatness of the land.

The shadow of the Saxon hero-king still walks there fitfully, reviewing the scenes of his youth and love-time, and is met by the gloomier shadow of the dreadful heathen Dane, who was stabbed in the midst of his warriors by the sword of an invisible avenger, and who rises on autumn evenings like a white mist from his tumulus on the hill, and hovers in the court of the old hall by the river-side, the spot where he was thus miraculously slain in the days before the old hall was built.

It was the Normans who began to build that fine old hall, which is, like the town, telling of the thoughts and hands of widely sundered generations; but it is all so old that we look with loving pardon at its inconsistencies, and are well content that they who built the stone oriel, and they who built the Gothic façade and towers of finest small brickwork with the trefoil ornament, and the windows and battlements defined with stone, did not sacriligiously pull down the ancient half-timbered body with its oak-roofed banqueting-hall.

Many scholars believe Gainsborough to be the basis for the fictional town of St Ogg's in George Eliot's The Mill on the Floss (1860).

The novelist visited Gainsborough in 1859, staying in the house of a shipbuilder in Bridge Street, which survives today as the United Services Club.

Two years later it bought the Trentside Works site and started to expand into many other areas, producing items such as starch, razor blades and sweets such as Cadbury's chocolates, its name appearing on the Roses selection.

By the east bank of the Trent near the railway bridge is a large mill owned by Kerry Ingredients (headquartered in Tralee).

Smiffy's were the only wigmaker left in the UK until December 2008, when bulk production moved to the Far East and over 35 jobs were lost.

Beside Riverside Walk are Whitton's Mill flats, which won a Royal Town Planning Institute award for the East Midlands.

[23] West Lindsey District Council had its offices at the Guildhall, Lord Street, but moved in January 2008 to a £4.3 million new-build in Marshall's Yard.

It serves the Brigg branch line and is the terminus of an hourly service to and from Sheffield on Mondays to Saturdays, calling at all stations.

On the second weekend in June in that year, the town hosted the Gainsborough Riverside Festival, an annual arts/heritage event that ran until 2013, when it fell to financial constraints.

There is a volunteer-run charity called Gainsborough Heritage Centre, with displays of a range of object from the town's past.

Unlike most of the UK, Lincolnshire retains a tripartite system, with secondary education for many pupils decided by voluntary examination at eleven.