Harrowby was a hamlet of two parts: Harrowby Within, and Harrowby Without – Harrowby Within now being part of Grantham civil parish, and Harrowby Without being part of Londonthorpe and Harrowby Without. Harrowby Hall is in the hamlet of Harrowby Without.
Harrowby is listed in the 1086 Domesday Book as "Herigerbi", with 18 households.
Originally a township of Grantham, Harrowby was created a civil parish in 1866, and in 1894 it was split into two separate civil parishes, Harrowby Within and Harrowby Without. In 1909 Harrowby Within was abolished and merged with the town of Grantham, and in October 1930 Harrowby Without was reduced in size to enlarge the town. In 1931 Harrowby Without was abolished to create Londonthorpe and Harrowby Without civil parish.
Lincolnshire is very low-lying and land had to be drained for agriculture to be successful. The larger drainage channels, many of which are parallel to each other, became boundaries between parishes. Many parishes are long and thin for this reason.
There is much fenland in Lincolnshire, particularly in the Boston and Horncastle areas. Fenlands tended to be extraparochial before the mid 1850s, and although many sections were identified with names and given the title "civil parish", little information has been found about them. Many appear to be abolished in 1906, but the parish which adopts them is not given in A Vision of Britain through Time. Note the WR category Lincolnshire Fenland Settlements which is an attempt to organize them into one list.
From 1889 until 1974 Lincolnshire was divided into three administrative counties: Parts of Holland, Parts of Kesteven and Parts of Lindsey. These formal names do not fit with modern grammatical usage, but that is what they were, nonetheless. In 1974 the northern section of Lindsey, along with the East Riding of Yorkshire, became the short-lived county of Humberside. In 1996 Humberside was abolished and the area previously in Lincolnshire was made into the two "unitary authorities" of North Lincolnshire and North East Lincolnshire. The remainder of Lincolnshire was divided into "non-metropolitan districts" or "district municipalities" in 1974. Towns, villages and parishes are all listed under Lincolnshire, but the present-day districts are also given so that places in this large county can more easily be located and linked to their wider neighbourhoods. See the WR placepage Lincolnshire, England and the smaller divisions for further explanation.