Dorchester is the county town of Dorset, England. A historic market town, Dorchester lies on the banks of the River Frome, in the Frome Valley, just south of the Dorset Downs and north of the South Dorset Ridgeway, that separates the area from Weymouth, south.
Further notes from Wikipedia
By 864, the area around Durnovaria/Durngueir was dominated by the Saxons who referred to themselves as Dorsaetas, 'People of the Dor' - Durnovaria. The town became known as Dornwaraceaster or Dornwaracester, combining the original name Dor/Dorn from the Latin and Celtic languages with cester, Old English for walled town. This changed over time to Dorncester/Dornceaster and Dorchester. The town was a thriving commercial and political centre for south Dorset with a textile trading and manufacturing industry which continued until the 17th century.
In 1613 and 1725 great fires destroyed large parts of the town, but some of its mediaeval buildings, including Judge Jeffreys' lodgings, and a Tudor almshouse survive in the town centre. Among the replacement Georgian buildings are many which are built in Portland limestone.
In the 17th century the town was at the centre of Puritan emigration to North America, and the local rector, John White, organised the settlement of Dorchester, Massachusetts. For his efforts on behalf of Puritan dissenters, White has been called the unheralded founder of the Massachusetts Bay Colony. (Some observers have attributed the oversight to the fact that White, unlike John Winthrop, never went to America.)
In 1833, the Tolpuddle Martyrs founded the Friendly Society of Agricultural Labourers. Trade unions were legal but because the members swore an oath of allegiance [to the union], they were arrested and tried in the Shire Hall which is preserved as it was at the time. Beneath the courtroom are cells where the prisoners were held while waiting trial. Dorchester Prison was constructed in the town during the 19th century and was used for holding convicted and remanded inmates from the local courts until it closed in December 2013.