The origins of trade and street directories can be traced to the 17th century but it was not until the late 18th century that they became common and not until the 19th century that they became really useful to the family historian.

They were aimed at the commercial, business and upper classes and it is these sections of society whose names are listed in them. Most of the directories follow a standard format with a brief history and description of the town or village followed by a list of the main inhabitants.

For example White's Directory of 1828 for Northumberland and Durham contain a list of Nobility and Gentry and the address at which they lived.  We discover that Cleadon Hall was the residence of Bryan Abbs esq, and the Rev Charles Thorp B.D, resided at Ryton Hall (7 miles west of Newcastle. Then we have a general history of the two counties, and the rates for each town followed by a list of public officers including Cuthbert Ellison MP (Hebburn) who was Deputy Lieutenant of Durham. The Gazetteer itself gives a description of the Parishes and the villages and Hamlets within the Parish. Some are very brief giving location and the main occupation of the inhabitants others are more detailed, but these earlier directories do not contain considerable amount of names as  the later ones.

From the middle of the 19th century directories begin to include street directories for larger towns. By the late 19th century the entries for major towns usually comprise a street by street listing followed by an alphabetical listing and a classified listing.

When using directories for family history purposes the directories list only around 40% of the households in any town or village. By the 20th century the street entries are much fuller with an entry for almost every house. Women are normally only listed if they were householders in their own right or ran their own business.  The last trade directory produced in this format was in 1974.

See the excellent free http://www.historicaldirectories.org/hd/index.asp