The following are suggestions but should not be interpreted as an exhaustive list. Make sure to research into the organizations publishing reports, etc.
While the terms data and statistics are often used interchangeably, they are different.
There is no single source / place where you can find data and statistics. This page of the guide will offer some resources for finding statistics and data related to incarceration, but you may need to do some more searching online.
One strategy you can use online is to add the words data or statistics to your search.
While including statistics can provide credibility to your argument, including faulty statistics can harm your argument. You need to evaluate the source of your statistical information. The following questions will help you to evaluate the reliability of statistical information.
Purdue OWL's Writing with Statistics guide is a great resource for helping you work with statistics in your writing.