To register in New Jersey, you must be:

• A United States citizen
• At least 17 years old, though you may not vote until you have reached the age of 18
• A resident of the county for 30 days before the election
• A person not serving a sentence of incarceration as the result of a conviction of any indictable offense under the laws of this or another state or of the United States.

Everything you need to know about voting and elections can be found here- https://nj.gov/state/elections/vote.shtml.