Statistics do not exist for everything: When looking for statistics it is important to ask yourself who is the information important to and who would collect the data? This will help you decide where to look for the data/statistics you need.
Example: A student is looking for the number of murders in Denver for the last 10 years.
Quick Start: Like all Government Information finding the statistic you want will very depending on who collected the data and what kind of data you want. Again Google is going to be good place to start, but make sure you add statistics as a search term.
Other Helpful Guides
These federal agency programs collect, analyze, and disseminate statistical data and information: