Is It Illegal to Sleep in Your Car? Federal, State and City Rules
Usually not. What can make it illegal: city vehicle-habitation bans, private lots, rest area limits, and being drunk in the driver’s seat. Rules explained.
Guides
Rest area and road trip guides: rules, planning, truck drivers, RV and car.
Can You Sleep at a Rest Area? Time Limits in All 50 States
Yes, in most states, in your parked vehicle and within the time limit. Here is the rule for all 50 states, with official sources, truck rules and plaza rules.