This new law comes after New York City recently passed a similar law and in 2005 a small town in Massachusetts raised the legal purchasing age, reportedly cutting smoking rates among young people in half.
"We are going to save a significant amount of lives," says Chair of Suffolk County Health Committee Dr. William Spencer.
Dr. Spencer sponsored the new Suffolk County Bill to stop young people from smoking before they start.
"This is a situation where we're talking about a developing brain, still developing into the 20s," says Dr. Spencer, "this legislation lets us address the issue that we can't address with education alone."
Government statistics show that 90% of adult smokers start smoking by the age of 18. It is also thought that adolescent brains may be more susceptible to addiction.
22-year-old Cheyanne Busso is trying to quit smoking and supports the new law.
"I started at 17-18, so to know my sister who's 11 will grow up in a county where that won't be available makes be proud and happy," says Busso.
Some critics argue that the law will be a violation of rights.
"You shouldn't have to be 21 - if you can go to war and vote, you should be able to smoke," says Suffolk County resident Andrew Chilott.
Meanwhile, lawmakers in neighboring Nassau County rejected a similar bill raising concern that people under 21 will go there to buy tobacco.
"It doesn't make any sense that Nassau should be a haven for young people to come to smoke, says Nassau County Legislator Judy Jacobs, "we have to get with the program."
The age restrictions in Suffolk County go into effect on January 1st. After that, businesses that sell tobacco products or electronic cigarettes to customers under 21 face fines of up to $1,000 for the first offense.