Castle Street takes its name from Hertford Castle, which still stands a few minutes' walk away. The castle began as a fortified burgh raised beside the River Lea by Edward the Elder in 912, to hold back Danish raids, and was rebuilt as a motte-and-bailey stronghold after the Norman Conquest. In 1216 it was besieged and taken by the French Dauphin, Louis; granted by Edward I to Queen Margaret in 1304, it became a royal palace and, at times, a prison that held two kings of Scotland and a king of France. Edward III gave it to his son John of Gaunt in 1360, and in 1563 Parliament and the courts moved here to escape the plague in London.

Its civic life came later. In 1911 the Hertford Corporation took a seventy-five-year lease on the castle from Lord Salisbury, at a peppercorn rent of two shillings and sixpence a year. The following summer the grounds opened to the public as gardens, with new entrance gates from The Wash given by Osmond Henry McMullen, and the gatehouse became the borough's council offices. Castle Street had settled into its role as the civic heart of the town.

For centuries the ground where Number 28 stands lay open. It was part of the long burgage plots that ran back from the old street frontages, used as gardens and yards, and it sat over the filled-in castle ditch, the levelled remains of the medieval moat. While the rest of Castle Street built up with medieval, Georgian and Victorian houses, this strip stayed clear, so when Hertfordshire County Council needed room for its expanding departments in 1925, it had a rare blank plot to build on. What went up was a deep-set Neo-Georgian office block of red brick, in the restrained, permanent-looking style local authorities favoured between the wars.

By the early 1950s the building had become the divisional office of the Hertford Division of the Hertfordshire Constabulary, with cells below; the old station at Queens Road was given up in 1954 as operations consolidated here. The police stayed until 1971, when the division moved to a new, purpose-built station in Ware Road. The county council kept the building in use after that, through to the 2000s, including as the town's electoral registration office, before selling it with vacant possession in 2010.

In 2011 the software company Lorensbergs made it their headquarters. They modernised the offices but kept the police past in plain view: old station photographs on the walls, a lantern by the front door, and a basement they still call the cells.

Number 28 is a working building again, home to several independent firms rather than a single institution. The council departments, the police division and the registration desks have all moved on, but its purpose has held steady: it was raised for the everyday business of the town, and that is still what goes on inside.

From the street it gives little of this away. It reads as a well-mannered interwar block of red brick, keeping company with the older houses around it and standing a short walk from the castle gardens it was built beside. A hundred years on, it does much what it was always meant to do, and does it quietly.