Is the second largest English county but one of the most thinly populated. The greater part of the county is flat but there are three parallel north–south ridges. Lincoln stands at the gap in the western ridge, the Lincolnshire edge, Louth at the gap of the eastern.
At the time of the Roman invasion, the region formed part of the territory of the Coritani. The Romans established a legionary base and then a colonia at Lincoln (Lindum) where the Fosse Way and Ermine Street intersected. Caistor was another Roman town of significance, possibly a spa. There were few obstacles to early Saxon settlement except in the south where salt marshes rendered the land impenetrable. Lindsey, in the northern part, may have formed a subkingdom, disputed between Mercia to the west and Northumbria to the north.
From the 870s onwards, the area formed part of the Danelaw, Lincoln and Stamford being two of the five boroughs. Many of the place‐names are of Danish origin—Grimsby, Saxby, Beckby, Swinthorp. The area was divided into three trithings—Lindsey, Kesteven, and Holland—and the largest, Lindsey, was further divided into three ridings. The smaller divisions known elsewhere as hundreds were in Lincolnshire called wapentakes. The shire itself seems to have been formed after 1016. The Domesday survey treated it as one unit.
In 1066 Lincoln was one of the leading towns in the country, with a population of about 5,000. Castles were built at Lincoln and Stamford and in 1072 the diocese was transferred from Dorchester to Lincoln. Barton did not long retain its importance, partly because the Great North Road diverted to the west from Ermine Street, bypassing the shire completely, partly because Hull took much of its river traffic. Boston, however, not mentioned in Domesday, developed rapidly and by 1204 was second only to London in subsidy payment. Louth and Sleaford, under the jurisdiction of the bishop, were just outside Lincoln's pull at 26 and 17 miles, and developed as local centres.
In the later Middle Ages a slow decline began. Stamford and Lincoln suffered much from the Black Death in 1349. A number of small harbours suffered from silting up of the coast. With the growth of colonies in the New World the whole axis of trade shifted towards western ports. Camden in 1586 wrote of the county largely in terms of past glories.
Tudor and Stuart Lincolnshire was little known or visited—a quiet county of small market towns. Its participation in the Pilgrimage of Grace in 1536 provoked Henry VIII to denounce its inhabitants as ‘the most brute and beastly of the whole realm’. Celia Fiennes in the 1690s noted that Lincoln's waterways were choked up, and 20 years later Defoe, while admiring the minster and the countryside, dismissed the town as ‘an ancient, ragged, decay'd and still decaying city’—if, indeed, it could be called a city.
The industrial developments of the 19th cent. helped to diversify the shire. Improvements in transport—turnpikes, canals, railways—helped to knit the shire together but did comparatively little to integrate it with the rest of the nation. Schemes for a main railway line north through Lincoln came to nothing and in the end the main line followed the Great North Road, almost bypassing the county. But the growth of an agricultural industry brought employment to Lincoln, Gainsborough, and Grantham. Grimsby opened its new dock in 1800 but its spectacular expansion followed the arrival of the railway in 1848, which benefited the fish trade. By 1901 it had overtaken Lincoln as the largest town in the shire. The discovery of iron in the north‐west of the county led to the development of a steel industry and the town of Scunthorpe came into existence: by 1961 it was the third largest town with 67,000 people. Rail transport and the cult of seaside holidays produced Cleethorpes, Skegness, and Mablethorpe with holiday camps and caravan sites.