Cyber Monday sales reached $3.45 billion, the largest online sales day in U.S. history, according to an online sales tracking firm.

Online sales rose 12.1 percent over 2015, according to data released Tuesday by digital software company Adobe Systems Inc., based in San Jose, California. The figure was 2.6 percent more than Adobe’s prediction.

“It’s an incredible milestone, but it’s also incredible that Black Friday inched so close to Cyber Monday this year, generating only $110 million less in online sales,” Tamara Gaffney, principal analyst at Adobe Digital Insights, said in a statement. “We’ll be watching this closely next year as Black Friday could be the one to top the records.”

New Yorkers came in second for online spending from Thanksgiving through Cyber Monday, at $1.1 billion, behind Californians’ $1.7 billion, according to Adobe.

Mobile spending generated $1.07 billion on Cyber Monday, a 34 percent increase from last year, but $130 million less than on Black Friday, Adobe found. Mobile devices accounted for 47 percent of visits to retail websites and 31 percent of sales, it found.

“Cyber Monday was a good kick to the holiday season,” said Marshal Cohen, senior retail analyst with the NPD Group, a Port Washington-based market research company. “We are seeing online start to mature and being a more integral part of the holiday experience.”

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On Long Island, local brick and mortar and online retailers also reported record-breaking online sales.

Farmingdale-based electronics giant P.C. Richard & Son experienced a double-digit percentage increase for Cyber Monday, the company’s chief executive Gregg Richard said. Televisions and appliances were the top selling items, he said.

“Cyber Monday was certainly our biggest day on the internet, although the entire weekend online and in our stores was very strong,” Richard said. “We posted positive gains each day with Cyber Monday being the highest volume.”

Fragrance.com, a beauty e-retailer based in Deer Park that sells designer fragrances and beauty products, said sales from Black Friday through Cyber Monday were up more than 20 percent. Company president Jason Apfel said the company processed more than 35,000 orders on Cyber Monday alone, with more than half of the traffic coming from mobile devices.

While Cyber Monday set a record, in-store retail sales decreased slightly on the Black Friday weekend. Thanksgiving Day and Black Friday in-store visits declined a combined 1 percent compared to last year, with Black Friday visits flat compared to 2015, according to ShopperTrak, a provider of shopper analytics based in Chicago.

The slight decline of in-store sales over the Thanksgiving weekend came from a combination of factors: shoppers spending less per person, retailers offering bigger discounts that led to customers saving, and consumers having more days to shop while still getting deals, said Thomas Shinick, an entrepreneurship and marketing expert and an adjunct professor at Adelphi University’s Robert B. Willumstad School of Business.

“The average dollar spending per customer was down about 3 percent from last year,” Shinick said. “People have more days to shop, so they are spreading it out.”

From Nov. 1 through Monday, online revenue totaled $39.97 billion, a 7.6 percent increase from last year, according to Adobe. The holiday shopping season is expected to generate $91.6 billion in online sales, Adobe said.