According to the timeline in the Appendices in the Return of the King, the Shire was settled by Hobbits in “1601 of the Third Age”, that being made Year 1 in the Shire Reckoning. It was at that time an uninhabited area of Arnor, designated as the King’s hunting grounds. Being as said King was too busy getting slowly crushed by the Witch King of Angmar to do much hunting any more, he decided the Hobbits were useful as a buffer population in the last need and allowed them to settle there. (The Appendix puts it rather more nicely, but it is easy to read between the lines. ;))
By the time of the events in The Hobbit, when we first see the Shire in narrative, it is about 1,300 years later and all four Farthings plus Buckland are populated with Hobbits, though the East Farthing is described as being the most densely populated.
So, just how dense is that? How many Hobbits are there, and how large is the Shire?
Here are the data points I can recall offhand, or look up with relative ease using Internet resources (not having my books close at hand):
[ul]
[li]According to this map of the Shire (presumably based on JRRT source material), it is roughly 150x200 miles in size, or about 30,000 square miles. That’s actually pretty large - about 3 times the size of the state of New Jersey![/li][li] They age more slowly than humans do, “coming of age” at 33 rather than 18 or 21. So every century is about three hobbit generations, making it about 40 generations of hobbits since the founding of the Shire.[/li][li] There is basically no immigration into the Shire; certainly not of Men (Saruman’s henchmen notwithstanding), and relatively little trade traffic (much less population flow) even to Bree where there is another population of Hobbits.[/li][li] Shire hobbits are homebound; few hobbits ever leave the Shire at all. As mentioned, for some time early on there was “much traffic” between the Shire and Bree, where there were other Hobbits, but by the end of the Third Age that had not happened very much for several generations - only a few adventurous Bucklanders now and then who would take in a pint at the Prancing Pony.[/li][li] They have large families. 5 or 6 children seems to be not uncommon. Certainly more than 2 children (the replacement rate) is the norm.[/li][li] They are not warlike; there is little attrition of the population due to conflicts with other hobbits, or Men or Dwarves or Orcs (thanks in no small part to the watch upon their borders by the Rangers). The last real conflict they had was nearly 200 years earlier, in the Long Winter, when a party of Orcs was repelled by the “Bullroarer”, Bandobras Took.[/li][li] They are not, apparently, routinely familiar with famine or disease. In the wake of that Long Winter of nearly 200 years ago, “many” died of famine (the “Days of Dearth”) but to what degree is unknown, and those days are a distant memory of hardship by the end of the Third Age.[/li][/ul]
So: we don’t know the original population size of Shire settlers, but if they were a fecund and circumscribed population at the top of the food chain bounded in a large region with no competition, it seems that they would grow pretty darn fast. Yet by all appearances the Shire is not densely populated.
Thought #1: Given that the Shire is relatively large yet also relatively sparsely populated, just how many hobbits are there in it at the end of the Third Age?
Thought #2: Given the optimal breeding conditions - comfortable and arable climate, plentiful supply of clean water, and (unbeknownst to them) sheltered from enemies - for a stretch of 1,300 years, why aren’t there more of them?
Thought #3: If the answer is that the Long Winter and the Days of Dearth took a very terrible toll on the hobbits, that would mean that most of the population of the Shire is descended from a small survivor group from about 180-200 years earlier. In which case… How inbred are the Shire hobbits?!
Maybe there was a wave of migration from Bree into the Shire about 175 years ago (after the Long Winter), since the hardships must have been as bad or worse out in Breeland, and perhaps the Shirefolk took in large numbers of their Bree cousins to help till the empty fields?