The following were historically ancient boroughs in the county of Dorset.
Boroughs, pre-Conquest
Bridport Dorchester Shaftesbury Wareham Wimborne Minster (see also Lapsed boroughs below)
Boroughs, post-Conquest
Blandford Forum (from 1605) Corfe Castle (from 1268 or 1576) Lyme Regis (from 1284 or -85) Melcombe Regis (from 1268) Poole (from 1248; a County of itself from 1571) Sherborne (from 1227) Weymouth (from 1252) (Weymouth and Melcombe Regis were joined as a double borough in 1571)
"Lapsed" boroughs Castleton (in Oborne) Charmouth Newton (in Studland) Stoborough (in Wareham Holy Trinity) Whitchurch Canonicorum Wimborne Minster
Sources Boswell, Edward, 1833: The Civil Division of the County of Dorset (published on CD by Archive CD Books Ltd, 1992) Hutchins, John, History of Dorset, vols 1-4 (3rd ed 1861-70; reprinted by EP Publishing, Wakefield, 1973) Mills, A. D., 1977, 1980, 1989: Place Names of Dorset, parts 1-3. English Place Name Society: Survey of English Place Names vols LII, LIII and 59/60