Strange_Kid, here's a really handy tool I use when planning out countries; The Domesday Book - Medieval Demographics Made Easy. You fill in your country's size in square kilometres, figure out your population density, then presto! It'll tell you most of what you need to know. You can probably ignore the bit about the hexes, as you're not using a hexagonal grid. The tool is keyed for medieval demographics, but you can use it as a rough guide for more modern places with a bit of research and tweaking.