In New Jersey, there is no recognized status of "separation." However, for those couples that for whatever reason have not proceeded with a divorce, you can put together a Property Settlement Agreement (PSA), sometimes referred to as a Marital Separation Agreement (MSA), to solidify the terms of your separation.
Whichever title you utilize, the purpose is to identify how you and your spouse will divide your assets, liabilities, child care, support, etc. Essentially it is a contract between the two of you, so that you both know what is expected of each of you. Assuming it is prepared properly, it can be enforced by a court. If you are contemplating such an agreement, you are strongly encouraged to seek the assistance of an experienced divorce attorney to help you prepare the agreement.
With all due respect, I have to disagree with the prior answers. They are not correct.
To answer your question, you do "need" to file for a "separation" before obtaining a divorce judgment - that was the law 50 years ago, but it isn't today. However, the functional equivalent of a "separation" is available in New Jersey. It is NOT a matter of "you're either marriage or you're not" in NJ.
New Jersey does have an equivalent to legal separation, called a "Limited Divorce" (or "Divorce from Bed & Board.") It is used most often in order to maintain medical insurance as spouses, which most policies permit (you have to check and see whether "legal separation" is "qualifying event" requiring the other person to be removed from coverage).
Below is a letter brief I submitted to the court on this topic, at the request of a judge who had recently been appointed to the Family Part and, like the previous responders here, didn't know a Limited Divorce was.
Dear Judge:
In October, I submitted a consent judgment converting the limited divorce entered into in this matter in 1994 to an absolute judgment. I received a call from your honor's law clerk indicating that the request should be refiled along with a memorandum of law briefly explaining the background of limited divorce (a/k/a Divorce from Bed & Board) as opposed to a regular (or "absolute" divorce), and the process of converting a judgment of limited divorce to an absolute divorce.
As indicated on the enclosed consent judgment, there is no opposition to this request. Mrs. Smith consents to the conversion of the judgment (it was originally entered to keep her on Mr. Smith's medical insurance; she now has her own employer-provided insurance). If there is any question about this, the Court can reach her personally at (732) XXX (work) or (732) XXX (home).
If the court has any further questions regarding this matter, please advise.
Statement of Facts
The parties to this matter were granted a limited divorce in November 2002. Plaintiff's insurance plan permitted him to continue defendant on his coverage for so long as they were subject to only a "limited" (rather than regular or "absolute") divorce. There was no additional cost to maintain her on said insurance.
Mrs. Smith has had her own employer-provided insurance for well in excess of a year and the parties have agreed to convert the judgment.
Legal Argument
I. THE COURT SHOULD ENTER THE ENCLOSED CONSENT JUDGMENT CONVERTING THE LIMITED DIVORCE TO AN ABSOLUTE DIVORCE.
Limited Divorce (also known as a Divorce from Bed & Board) is permitted by N.J.S.A. 2A:34-3, which provides:
Divorce from bed and board may be adjudged for the same causes as divorce from the bonds of matrimony whenever both parties petition or join in requesting such relief and they or either of them present sufficient proof of such cause or causes to warrant the entry of a judgment of divorce from the bonds of matrimony, provided further that in the case of a reconciliation thereafter the parties may apply for a revocation or suspension of the judgment, and provided further that the granting of a bed and board divorce shall in no way prejudice either party from thereafter applying to the court for a conversion of said divorce to a divorce from the bonds of matrimony, which application shall be granted as a matter of right.
A judgment of divorce from bed and board decrees a judicial separation, but does not terminate the bonds of matrimony. Weinkrantz v. Weinkrantz, 129 N.J.Super. 28 (App.Div. 1974), Mueller v. Mueller, 95 N.J.Super. 244 (App.Div. 1967). The entry of a divorce from bed and board permanently fixes the property rights of each party against the other. Lavino v. Lavino, 41 N.J.Super. 608 (Ch.1956), affirmed 23 N.J. 635, Loechner v. Loechner, 119 N.J.Super. 444 (Ch.Div. 1972).
... out of space - will submit remainder as a comment.