All of the core compilations of federal statistics are available online. However, this is current information. If you need historical statistics, from earlier than 1995, you will probably need to consult the print and microfiche collections of government publications. Also, each agency independently creates their Web sites, so actually finding information on the Web site can be tricky at times, not to mention the fact that the look and content of the site is constantly changing. Look for words like publications , data , information , library , or resources to find statistical information.
Most sites do have a search engine as well.
The Census of Agriculture is conducted by NASS every five years to collect information on the number of farms, land use, production expenses, etc.