The length of Berkshire on an east and west line is 41 miles. It may be described as a rectangle with a somewhat square projection at the south-eastern corner. Ashmole compares it to a lute and Fuller to a slipper. The northern boundary is practically formed by the river Thames, and is in consequence most irregular. Where the river curves in a southerly direction, the width of the county is contracted until it is less than seven miles at Reading. Until 1844 Three Mile Cross and the country between that place and the Hampshire border was an outlying part of Wiltshire, so that the width of Berkshire at Reading was less than four miles. This little bit of Wiltshire has however now been joined to Berkshire.

Berkshire as it is shown upon most maps is known as the “Geographical” or “Ancient County” of Berkshire, and its area is 462,208 acres, that is about one-seventieth of the area of England.

For administrative purposes the boundaries are slightly different, and the area of Administrative Berkshire including the county borough of Reading is 462,367 acres. By deducting from this the area under water, i.e. rivers, ponds, lakes, etc., we arrive at the figures 459,403, which are used as the area of Berkshire in acres for the purpose of agricultural and other returns issued by Government. The county of Berks for registration purposes, that is for Parliamentary elections, etc., includes all the Administrative County and also Egham in the east, Culham and Crowmarsh in the north-east, small bits of Oxfordshire and Gloucestershire in the north, and the rural district of Ramsbury in the west, giving a total area of 573,689 acres.

Berkshire was, as we have said, a part of the Saxon kingdom of Wessex, and it has inherited from that kingdom its northern boundary, the river Thames. It is interesting to note that some rivers have been selected as boundaries to a much greater extent than others. Thus the Thames forms a county boundary for a great part of its course, whilst the river Severn flows through the middle of counties.

The Thames forms the county boundary at Old Windsor from a point a little above Magna Charta Island and separates Berkshire from Buckinghamshire, and later on from Oxfordshire, the boundary sometimes running in midstream, sometimes on one bank, and sometimes on the other bank. Near Oxford the boundary passes for a short distance a little to the west of the river, that is on the Berks side. The Upper Thames or Isis becomes the boundary between Berkshire and Oxfordshire, and then for a very short distance between Berkshire and Gloucestershire, until near Buscot the river Cole joins the Isis and the boundary turns in a southerly direction near to the bank of the Cole, the adjoining county being then Wiltshire. The county boundary runs by or close to the river Cole to near Bourton, and it then crosses the chalk country with no definite marks. At one point it crosses an old earthwork, Membury Fort, and reaches the river Kennet a little east of Chilton Foliat. From this point to near Woodhay, a distance of some 14 miles, the boundary of the county for administrative purposes differs from the boundary of the ancient or geographical county (see page 9), indeed considerable alterations have been made in this part of the county boundary at various times. The present administrative boundary after crossing the Kennet, turns in a westerly and then in a south-easterly direction following the border of Hungerford and Inkpen parishes and runs on to a point at the south-western corner of Combe parish where Berkshire, Wiltshire, and Hampshire meet. The Berkshire boundary then runs west to Pilot Hill and then turning takes a northerly or north-easterly course until it reaches the stream Emborne which it follows for several miles until near Brimpton the stream bends sharply northwards to join the river Kennet, while the county boundary continues its easterly course through a forest country to the Imp Stone plantation. It then makes a wide detour to the north leaving Mortimer West End and the Roman town of Silchester in Hampshire. This part of the boundary has at more than one date been subject to alteration and for a time it ran close to Silchester and is thus marked on many maps. Stratfield Mortimer is in Berkshire, and about a mile to the east of Silchester the county boundary reaches a Roman road which it follows pretty closely for a considerable distance, crossing the river Loddon at Stamford End Mill. On the east of the Loddon we come to a small tract which, until modern times, was an outlying part of Wiltshire, bounded in part by Berkshire and in part by Hampshire. It is now included in the former county, and the Berkshire boundary continues its easterly direction on or near the Roman road until it reaches the stream Whitewater close to its junction with the Blackwater. The county boundary reaches the latter river close to a ford, no doubt a well-known place, for these fords are in most cases very old crossing-places and this one certainly goes back to Roman times and may very likely have been used in still earlier days. The boundary then turns along the Blackwater, and though it does not always follow the present course of the stream, it keeps near to it for some eight miles, until we reach the Blackwater Bridge on the London and Southampton Road. This is another ancient crossing-place, and here the counties of Berkshire, Hampshire, and Surrey meet. The Berkshire and Surrey boundary now runs in a north-easterly direction, through the grounds of the Royal Military College, Sandhurst, up a small stream to a place named Wishmoor Cross, possibly the site of a cross in former days, and evidently a well-known place, for five parishes meet there. From this point the boundary crosses the forest district of Bagshot Heath, celebrated in connection with highwaymen, and eventually reaches the Thames near Old Windsor.

In old maps it will be noticed that there are detached portions of Berkshire surrounded by Oxfordshire, and also detached portions of Wiltshire partially or wholly surrounded by Berkshire, but in modern times the county boundaries have been much modified for purposes of convenience. Thus an Act of Parliament was passed in 1844 to annex detached parts of counties to the counties in which they are situated. This Act transferred from Wiltshire to Berkshire parts of the parishes of Shinfield, Swallowfield, and Wokingham. Shilton and Little Faringdon were transferred from Berkshire to Oxfordshire, and part of Inglesham was given to Wiltshire. The boundaries of counties were still further simplified by an Act of Parliament of 1887, one of the objects of which was to arrange that no Union, Borough, Sanitary District, or Parish should be in more than one county.