Emerikol
Legend
Yes. 1000AD is as late as I would go and 500AD is possible. These are just numbers I've gotten off the internet so if they are wrong then I stand corrected.That's really low, unless you're talking about the Dark Ages. The population of England in 1086, at the time of the Domesday Book, was 1.5 million. England is almost exactly 50,000 square miles, so that's 30 people per square mile at that point. By 1300 (after 200 years of a good, warm, stable climate that allowed populations to boom), the population had grown to 4 to 5 million, which amounts to 80 to 100 people per square mile, before the Little Ice Age and the Black Death dropped the population significantly (but not anywhere near the 1086 level). France is similar, with about 50 people per square mile in 1100, and 100 by 1300.
What I see after some more searching is 500AD is 3.7, 700AD is 13.3, and 1000AD is 18.6. So you could pick what you want but it does seem Greyhawk is very dark ages.