The term originated in France (bailie being the Old French term for a bailiff). Under the ancien régime in France, the bailli was the king's representative in a bailliage, charged with the application of justice and control of the administration. In southern France, the term generally used was sénéchal (cf seneschal) who held office in the sénéchaussée. The administrative network of baillages was established in the 13th century, based on the earlier medieval fiscal and tax divisions (the 'baillie') which had been used by earlier sovereign princes (such as the Duke of Normandy). (For more on this French judicial system, see bailli, prévôt and Early Modern France.)
A bailiwick (ballei) was also the territorial division of the Teutonic Order.
In English, the original French bailie was combined with '-wic', the Anglo-Saxon suffix meaning a village, to produce a term meaning literally 'bailiff's village' - the original geographic scope of a bailiwick. In the 19th century, it was absorbed into American English as a metaphor for one's sphere of knowledge or activity.
The term survives in administrative usage in the Channel Islands, which for administrative purposes are grouped into the two bailiwicks of Jersey (comprising the island of Jersey and uninhabited islets such as the Minquiers and Écréhous) and Guernsey (comprising the islands of Guernsey, Sark, Alderney, Brecqhou, Herm, Jethou and Lihou). Each Channel Island bailiwick is headed by a Bailiff.