The French Government have placed on-line the results of the 2004/5 national census, with an analysis of the results by 'commune' and by metropolitan area.
You can find out the total population of an area by age and gender and the length of time people they have lived there, their marital and employment status, the number of owner occupiers and tenants, the number of vacant properties, and the age, type and overall condition of property. Perhaps of greatest interest to many, you can also find out the number of those with second homes in the commune, although not by nationality! The results are presented in a range of colourful and easily digestible graphics and make interesting reading for anyone on the cusp of buying in the country. You can view the information by visiting France Census.