For most of its history Sleaford was not Sleaford the town, it was Sleaford the property. The Bishops of Lincoln held it in the medieval period, granting the right to hold a fair in 1136 and a market between 1154 and 1165 confirmed by Edward III in 1329. The town's freedoms were never formally chartered because the bishops did not want them to be. When the Crown took the manor after the Lincolnshire Rising of 1536 - the local revolt led by John Hussey, executed for his part - it sold the lands to Robert Carre, a wool merchant from Northumberland who had settled in Sleaford a decade earlier. The Carres became gentry. The Carre heiress married the Earl of Bristol in the late 17th century, and the Hervey family of the Earls and Marquesses of Bristol owned most of Sleaford until 1979. They collected tolls on the market. They charged for driving cattle through the town. They controlled the land on which the town might have expanded, and for centuries it did not.

Sleaford caught up in the 18th and 19th centuries. The River Slea was canalised, opening as the Sleaford Navigation in 1794, easing the export of farm produce to the Midlands and bringing in coal and oil. Wharves were built around Carre Street. Tolls increased twenty-sevenfold in seven years. Then in 1857 the railway arrived from Grantham, and the new technology promptly began killing the old one. Navigation income fell 80 per cent in a decade. The canal was abandoned in 1878. Industrial Sleaford emerged from the railway age: the Bass Maltings, two competing seed merchants - Hubbard and Phillips, and Charles Sharpe - the latter trading in the United States and Europe by the 1880s. Kirk and Parry opened a steam-powered flour mill in 1857. Ward and Dale built steam cultivators. By the end of the century Sleaford had a gasworks, a Local Board of Health, a workhouse on the edge of town, and slums around Westgate that the General Board of Health called crowded, unsanitary, and disease-ridden.

Then, in 1979, the Marquess of Bristol went broke. Victor Hervey, the 6th Marquess, had spent extravagantly and accumulated debts that could only be paid by selling the family estates in Sleaford and Quarrington. The estate office closed in 1989. The land went to developers. From 1981 to 2011, Sleaford's population more than doubled - the fastest growth of any town in Lincolnshire in the 1990s. The A17 bypass opened in 1975. The A15 bypass came in 1993. A one-way system was tried in 1994 and is still complained about. Modern Sleaford works as a commuter town for Lincoln, Grantham, and Newark-on-Trent, with major RAF employment at nearby Cranwell, Digby, and Waddington. The Bristol Arms Arcade opened in 1958, the Riverside Centre in 1973. Twenty-one per cent of the town's workforce is in retail and hospitality; thirty-seven per cent in public administration, education, and healthcare. The new estates spread out across what used to be Hervey pasture.

Old Sleaford is a different walk from new Sleaford. Cogglesford Mill still grinds, the only working medieval mill on the Slea, with a working watermill mechanism visible to visitors. The Black Bull on Southgate is the kind of low-beamed pub that has stood through every century the town has had. The Northgate market still happens on Fridays, Saturdays, and Mondays as it has for centuries, with a farmers' market added on the first Saturday of the month. St Denys' Church holds the tomb of Sir Edward Carre, who died in 1618 - the founder of the family that bought the town from the Crown and never quite let go of it. And on the north-eastern edge of town, beside the railway line that killed the canal, the Bass Maltings still stand: empty, magnificent, waiting for a use that the 21st century has not yet been able to invent for them.