Listed below by state is the Age/Height/Weight requirements for use of a car or booster seat. The chart is written in such that a child must use a car seat until the listed weight and height and age. If an entry is blank, that state law does not have that requirement.
If the age or weight or height is the same for a car seat and a booster, then the state indicates that a booster OR car seat must be used until that age / weight / height, but they have left it up to the parent and seat guidelines to determine which is appropriate.
The info below is merely a guideline, it was gathered from state web sites. The web site used can be found by clicking on each state's name. State laws are constantly changing; therefore:

IN NO WAY SHOULD YOU RELY UPON THIS CHART AS A REPRESENTATION OF CURRENT LAW!

Currently, there is a major push to enact laws that require children to be in a booster seat until the age of 8 or 80 lbs. As a general rule: Rear facing car seat / infant car seat until 1 year old and 20 lbs. Car seat until 4 years old and 40 lbs. Booster seat until 8 years old and 80 lbs.

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