The Poor Rate Books and Parish Vestry Minutes are often overlooked, but can be quite useful for the family historian.

They arose from the way that the parish was administered. 

Until well into the 19th century, the Church of England parishes were the main organisational unit for local government. The parish church was the administrative centre of the parish and the church Vestry was the traditional meeting place where the parish business was conducted. As a result the the meetings to conduct business came to be referred to as Vestries, and the notes recording the business that was conducted were called Vestry Minutes. Many of these record books have survived and they are generally held by the relevant County Record Offices.  Some of the more mundane business was also recorded in separate books, in particular the church accounts and the parish accounts.  The latter include the Poor Rate books which recorded the income from the Poor Rates.

Amongst the duties of the parish officers, as mandated by the various Poor Laws, was care of the poor of the parish, i.e. those that for one reason or another could not provide for themselves. Some of these people only required a little temporary help, for example if the main wage earner of the family could not work due to injury, but in other cases permanent help was needed, e.g. for the old and infirm and for the physically and mentally handicapped.

Help was administered in two ways: Outdoor Relief (sometimes known as Out Relief) was simply money, food or clothing given to the poor where they lived. The other was Indoor Relief, which was provided as board and lodging in the local poorhouse (or workhouse). 

On the Isle of Wight small workhouses were present in the parishes of Northwood (from 1728), Brixton (now known as Brighstone) and Newport (both from 1729), but workhouses were generally too expensive to be maintained by a single parish so in 1770 an Act of Parliament was passed incorporating all the parishes of the Island into a union that could build and maintain a single workhouse, or House of Industry as it became known, for them all. This was built on the site that is now St. Mary's Hospital. Significant parts of the House of Industry remain as parts of the hospital.

The expense of all the relief had to be covered by the individual parishes.  This was the purpose of the Poor Rates. This was a system whereby every householder contributed according to the assessed rental value value of their property. The rates were generally collected quarterly. For example: if a rate was set at 9d per £, then a householder in a property valued at £20 per annum would have to pay 9 x 20 = 180d (or 15 shillings).

The Poor Rate Books record these assessments and income for the parish. They usually give the names of all the heads of household along with the amount of rates they were paying.  Parish Registers of Baptisms, Marriages and Burials don't usually note where people were living within the parish so the information in the Poor Rate Books can be very useful to confirm exactly where and when a family was living in a parish. Here is an example from Calbourne in 1810:

As can be seen, for the Quarter from Lady-day to Midsummer 1810 the rate was 7d in the pound, and therefore Richard Arnold of Newbarn had to pay £11 13s 4d on his total rents of £400.

In contrast Vestry Minutes cover all sorts of parish business. Much of this is of little interest to the family historian but it does sometimes include bastardy and settlement issues. Here is an example from Arreton in 1753:

This gives confirmation that Robert Rayner, the father of Robert Rayner (who was the father of Mary Bagsters' child) has given "good and sufficient security of indemnification". i.e. He has guaranteed that the parish will not have to pay relief for the child, and therefore Robert Rayner (junior) is "att full liberty to walk where he pleases"!

Another example from the Arreton Vestry Minutes a little later:

It appears that "Mary Noris's Son a bastard and David Elsbury and his family" have become in need of parish relief but do not belong in the parish (i.e. they have no claim to be settled there) and therefore settlement orders are to be sought to remove them to their respective home parishes.

Both Poor Rate Books and Vestry Minutes are generally included with other parish records at the local County Record Office. The Isle of Wight Record Office (IWRO) parish record holdings are available at https://www.iwight.com/Residents/Libraries-Cultural-and-Heritage/Records-Office/Parish-and-Non-Conformist-Records/Parish-Records-and-Registers. The list of parishes there gives the dates covered by the parish registers for Christenings/Baptisms (C), Marriages (M) and Burials (B) but if you click on the parish name it will give a pdf file listing all the parish records, including Vestry and Poor Rate records if they exist.

As far as I am aware, none of the Isle of Wight Poor Rate Books or Vestry Minutes have been filmed, digitised or even transcribed. The only way to check them is to go the IWRO and physically read through them (or of course I could do this for you!). Obviously, this will be a very time consuming process unless you have a reasonably good idea of which parish and time period your relative lived in.

Happy hunting!