How America Gives is an incredible resource for determining how charity is viewed today by the people of the United States. The study is based on exact dollar amounts released by the Internal Revenue Service showing the value of charitable deductions claimed by American taxpayers. It is not based on extrapolations from spot surveys or statistical models. The rankings show the percentage of their income that households donated from the money they had left after paying their taxes and covering housing, food, and other essential expenses.
You can see down to the zip code what percent of income is given, the average contribution size, the average discretionary income, and the total returns issued. It also breaks down the data by salary group.