Camping on someone's private property does constitute trespassing.
In more populated areas it may bring a visit by the county deputy at 3 a.m.
Or by a landowner who doesn't look too kindly on people who set up camp.
That is why many people "stealth" camp. Which I think is a bad idea.
You can camp most anywhere on federal public lands - BLM, USFS.
Doesn't apply to national parks, military bases, wildlife refuges.
Many states permit random camping on some state lands.
In the Great Plains, many small towns will let you camp in the town park.
In general, it gets easier to random camp the futher west you go.
Until you get to the West Coast. Where state park have cheap hiker/biker sites.
Be aware that random camping may leave you vulnerable to harassment.
Sometimes it's just bored kids, but other times it can get dicey.
If you must camp by the side of the road -
Choose a public unpaved road and ride a half mile or so off the highway.
A two-track leading into a farm field is usually hard-packed and bare.
But you should only set up in the road right-if-way -
And wait until almost dark and be gone by first light.