Hi KandT,
Boondocking means different things to different people, but I am assuming you mean no-hookups, low-cost (or free) camping. If you do some extensive web searching, you will find some good info, but it takes some patience and a lot of clicking around to find current and accurate information about exact places, prices, rules, etc.
Many federal and state owned lands will allow "dispersed camping" which is basically "boondocking". It is low cost (free in some cases) and usually in areas that are more remote or off the beaten path. Some national forests and state wilderness lands will allow camping for hunters or equestrian use. These equestrian-use areas will often allow small RV's to camp - there is no electricity at such sites, but water hookups are often available. Costs can range from free to $15 a night or so. You maximum stay also varies, but is usually no less than 14 days, and is often 30 days or more, but sometimes the stays must be non-consecutive at some point before it can be renewed.
Look for Federal stuff - Bureau of Land Management, National Forests, etc. Also look for state Forestry department lands, wildlife management areas, and nature preserves. Many will allow "no trace" dispersed camping.
Find the area you would like to boondock in or around, and start looking up county and state websites for camping. Move up the food chain from local government, county, state and then federal. Lastly but not least, the Army Corps of Engineers has many facilities across the country that offer low-cost camping and some of them have hookups and amenities.
Good luck and safe travels.