Gun retailers across Maine and the nation expected interest in firearms to spike after the shooting in Newtown, Conn., on Dec. 14, and they were right.

Recently released FBI data shows that firearm background checks initiated through the National Instant Criminal Background Check System increased in all 50 states from November to December.

In fact, the number of background checks in December was the highest in any month since the system was started in 1998.

The average increase per state was 41 percent, and 17 states recorded increases of at least 50 percent, led by Georgia, which processed 66 percent more background checks in December than it did in November.

Maryland had the smallest increase, 12 percent.

Maine’s increase of 36.5 percent was its biggest month-to-month jump since 1998. A total of 12,416 background checks were initiated in Maine last month, an increase from 9,094 in November.

The number of background checks does not correlate exactly with gun sales. The FBI data does not indicate how many people fail background checks or the number of guns purchased with each check. Also, private sales and sales at gun shows are not always subject to background checks.

Still, the FBI data clearly shows a spike in the number of people buying guns in the wake of the Connecticut shooting that killed 27 people, including 26 at Sandy Hook Elementary School in December.

Shortly after the shooting, Jeff Weinstein, president of the Maine Gun Owners Association, said gun sales always increase after incidents of mass violence.

“It’s a reminder that it’s a rather violent society,” he said. “People don’t just jump out and buy a gun. They’re already thinking about it.”

Last month’s increase mirrors spikes after past gun-related events, according to FBI numbers.

Other events in 2012 increased interest in guns, including the shootings at a movie theater in Aurora, Colo., in July and the re-election of President Barack Obama, which many conservatives saw as a threat to gun rights, even though Obama hadn’t pushed for gun control in his first term.

In Maine, the number of background checks for gun purchases has been growing steadily since 2008.

From 2003 through 2007, the annual number fluctuated between 50,000 and 53,000. By 2009, it eclipsed 60,000. By 2011, it increased to 73,127.

Last year, the total was 91,834, an increase of about 80 percent within the last decade.

Nationally, background checks have followed a similar upward trend.

“I think gun owners pay close attention to politics, and we’ve had an uptick in Maine ever since Obama was elected,” said George Smith, a lobbyist in Augusta who was director of the Sportsman’s Alliance of Maine, and also writes a column for the Kennebec Journal and Morning Sentinel.

Last month’s school shooting gave the administration both the public support and the political muscle to address gun control, although there is no guarantee that any major changes will be made.

In Maine, the shooting spurred talk of gun control at the local level. Portland officials, including Mayor Michael Brennan and Police Chief Michael Sauschuck, will host an event Monday at City Hall to introduce a national TV ad featuring family members of victims of gun violence, demanding a plan of action from political leaders.

Among other things, the ad calls for a requirement that every person who buys a gun pass a criminal background check.

Smith said most gun owners support background checks. In fact, he said, one of the main reasons for the steady increase in checks over the last several years is the effort by groups like Project Safe Neighborhood to encourage them for private gun sales.

Some gun retailers in Maine, including L.L. Bean and the Kittery Trading Post, will do background checks for private sellers for a nominal fee.

“It’s well worth it, in my opinion,” Smith said.

Jasen Pelletier at Hussey’s General Store in Windsor said he has been asked to do a background check on a private sale just once or twice. “Most private sellers will just go ahead and sell and save the $30,” he said.

In general, December is a busy month for background checks because of Christmas sales.

In the last decade, the average increase in background checks from November to December has been about 19 percent nationally.

In Maine, with exception of 2012, that increase has been much smaller. In some years, the number has decreased from November to December.

October, historically, is the busiest month in Maine because it is immediately before hunting season, Smith said.

“We get a boost at hunting season and then we get a holiday boost,” Pelletier said. “In mid-February, things pick up once people get tax refunds.”

Asked whether he expects to see a surge when the Obama administration proposes new gun control measures, he said, “I don’t know what’s left to see. Most of those popular guns and ammo have been wiped out.”