The sparse upland landscape of Forest-in-Teesdale and Frith lies above High Force in Upper Teesdale. The parish is mainly moorland spread out between the Tees, to the north, and Lundedale Forest to the south.

Although this area is only sparsely occupied today, there are many remains from earlier periods to show that people have long been living in this part of the North Pennines. The earliest evidence for activity in this area dates to as early as the Mesolithic period, over 10,000 years ago. A number of flint tools of this date have been found near High Force. These are likely to be all that survive of a temporary hunting camp. At this time there were no permanent settlements, instead people travelled across the landscape, hunting wild animals and collecting wild plant. It is thought that in summer they would have travelled to upland areas like Upper Teesdale to hunt animals such as deer and wild cattle. They may well have also caught fish in the nearby river. As the weather got worse toward winter these small communities would have moved back down to lowland areas.

By the Neolithic the first farming was beginning, with crops being grown and animals domesticated. However, in upland areas like this, where the weather was more harsh, it took a while for farming to develop. Nonetheless, people would have continued to visit this area to use its natural resources. By the Bronze Age more permanent settlements would have become common. A bronze axe of this date has been found at Dineholm Quarry. This axe may have been used to cut down trees to help clear land for the earliest farming. There was certainly permanent settlement by this point. Although no actual settlement sites have been discovered, a burnt mound found near {Widdybank Farm D5152}, was probably the location of either a religious ceremony, or more mundanely, a communal cooking site.

By the Iron Age people were beginning to live in simple enclosed settlements containing several round buildings. Typical examples have been found at {Forcegarth Pasture D3108}. These are of Roman date, but similar types of settlement would have been typical in the Iron Age. This shows how little effect the arrival of the Romans in the 1st century AD.. Although some Roman coinage has been discovered in this area - a 4th century coin hoard was found near High Force. It is likely for that most people life continued as normal. It is possible that the Roman army carried out some lead working in the area, though there is no hard evidence for this.

The Roman's left in the early 5th century, but again there is little evidence for significant levels of settlement. Although some Anglo-Saxon settlement is known nearby at Simy Folds, but there is no evidence of such occupation in the area. It is noticeable that unlike many areas the only settlement here, Forest, does not have an Old English placename, suggesting that it was founded sometimes after this date. Indeed very little is known about this area during medieval period either. There was undoubtedly medieval lead mining in the North Pennines, but no firm evidence for this has been found in Forest, though it is possible that a heap of iron slag on the north bank of Hag Sike may be the remains of medieval iron working. Most of the population were probably involved in upland hill sheep farming. At this period, the flocks of sheep were often brought up from the lowlands during the summer to graze on the moors. The shepherds would have lived in simple huts known as shielings

It is really in the 18th and 19th century that Forest begins to have a siginificant population. As in previous eras, the area was still dominated by sheep farming, and growing small amounts of crops. The remains of this agricultural landscape can still be seen across the moors. Many 19th century sheepfolds can still be seen; in fact some of these are still in use in the 21st century. These aren't the only remains related to sheep farming, for example the sites of sheep washes are known at Cronkley and Washpool Scar. Other remains include the {stack stands D4134} at Chester Sike. These were used to keep food for the livestock off the wet ground in this rainy era.

Although farming was widespread in the 19th century new industries developed. At Cronkley Scar a pencil mill was built- it worked from about 1847 to 1889, and was deserted by 1890. It was used to make simple pencils from the locally quarried slate. The main industry though was lead mining, which grew in the late 18th century, and was mainly run by the London Lead Company, which had its main regional headquarters at nearby Middleton-in-Teesdale. It was the Company which was responsible for constructing the main turnpike road from Middleton to Alston, which ran through Forest. Lead mines were built at {Silverband D4462} and {Chester Sike D4134} and the remains of levels, shafts and hushes can still be seen. The rise in importance of lead mining led to an increase in the population. The area, which had earlier been part of the parish of Middleton-in-Teesdale, became a separate parish. The church of St James, which had previously been a chapel relying on the main church at Middelton, was built in 1849. The lead mining industry died out by the early 20th century, and Forest returned to its quiet agricultural life. Farming still dominates the area, though the rise of tourism has also had a noticeable effect. An old farm has been turned into a Youth Hostel, and many people now visit the area to walk in the beautiful surroundings.

There are a number of war memorials located in various buildings around the parish, one of which is quite unique. In the Methodist Chapel of Forest-in-Teesdale there is an electric light, the installation of which was carried out as a commemorative gesture to the memory of a WW2 airman from the village, whose body was never found following a crash. Other memorials can be found within Forest Primary School and the Church of St. James the Less at Langdon Beck that are dedicated to those of the parish who fought and died in the First World War and later conflicts.