Perhaps the situation in my aea might help shed some light on the subject as well
here the vast majority of old barns date from roughly the same period, most built from about 1890 to about 1920 at the latest
The oldest barn I have come across in our particular county was built in the 1870's there are older buildings, mostly log cabins that were re-purposed later on after a permanent house was built. It is possible that there were some smaller barns built in the early days of settlement, but these were either dismantled or incorporated into bigger barns in some way. It is common to find some recycled parts in many barns that are clearly much older than the barns themselves.
Now there is a reason why there are few barns from before the 1890s. Settlement around here began in the 1840s, then once things got going the civil war popped up. in the 1870's, when the situation might otherwise have turned around and been good for new barn building, the country got hit by a major depression, and wouldn't recover for some time.
The last decade of the 19th century saw a major economic boom, and that I think is why there are so many barns built beginning in this period.
These barns are all timber framed, and some of them are totally hand hewn, some might have braces come from a sawmill, and others the shorter members might be sawn. The restriction was the size of the sawmills, which in general were not long enough to handle the longest timbers needed, often with an upper range of maybe 20 to 25 feet. so by necessity, hewing was employed.
things built after perhaps 1920 tend to not be very well built, and after that there is virtually no timber framing done any more.
