Municipal Judge Debra J. Gelson suspended 60 days of the sentence providing Smith performs 500 hours of community service consisting of visiting sick children at hospitals.
Smith, who grew up in this town about 20 miles east of Trenton, was taken to county jail Tuesday night to begin serving his sentence.
"He's 23 years old; he's a tough kid and he's going to do these four weeks and come out a better person," said Kevin Hextall, an attorney representing Smith.
Gelson also suspended Smith's license for two years, to begin next March after Smith's current license suspension expires.
Smith, who didn't comment after the sentencing, expressed regret at causing the accident that killed his friend, 21-year-old Andre Bell of East Orange, in June 2007.
"It's been unbearable to deal with," he said to the court. "I am deeply sorry. I never intended for this to happen. It tears me up that it went down like that."
Nuggets vice president of basketball operations Mark Warkentien released a statement Tuesday night.
"We will continue to support J.R. during this difficult period and will have no further comment at this time," he said.
Andre Young Jr. was found dead by his mother at his Los Angeles home after spending a night out with friends.
After toxicology and other tests, the coroner ruled his death as accidental and says the case is closed, spokesman Larry Dietz said on Friday.
The 61-year-old former football star could spend the rest of his life in prison. Sentencing was set for Dec. 5.

Gonna go with Travis and Tyler to see Get Smart before we all go into work. I wish I could get more people together, but a lot of people are working.
Durant averaged 20.3 points per game in 2007-08 -- the highest scoring average for a rookie since Carmelo Anthony averaged 21 points per game and LeBron James averaged 20.9 ppg in 2003-04. Only three of the past 10 rookies of the year -- Durant, James and Elton Brand -- have averaged at least 20 points in their first season.
"Most of the players in the league use marijuana and I have and do partake in smoking weed in the offseason sometimes," Howard told "The Michael Irvin Show" on the local ESPN affiliate. "I mean, that's my personal choice and my personal opinion, but I don't think that's stopping me from doing my job."
Despite suffering a torn tendon and broken bone in his pinkie, Kobe Bryant will play in Sunday night's NBA All-Star Game, according to a Lakers spokesperson.
Bryant suffered the injury -- initially described as a dislocated pinkie -- on Feb. 5 against New Jersey. The Lakers disclosed Thursday that the damage was more extensive than first thought. The injury included a torn radial collateral ligament and an avulsion fracture in the pinkie.
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