If you’re registered to vote, your mailbox probably has been inundated with political advertisements recently. And then there are all those attack ads on the radio and TV.

The unprecedented election spending this year largely is a result of independent groups, unfettered by legal limits on how much money they can raise.

In just three legislative districts in Central Jersey, combined spending by the state Senate and Assembly candidates, the two major state parties and the independent groups has topped $5 million, according to a Courier News and Home News Tribune review of state campaign finance documents.

That total doesn’t include spending on county and municipal campaigns or the spending by an independent group funded by the state’s largest teachers union, the New Jersey Education Association.

That group, Garden State Forward, has reported spending $4.25 million in this election, but the group did not disclose in its state filings how much it has spent in each of the eight races where the group has taken sides. NJEA spokesman Steve Wollmer said a breakdown of the spending was not available Wednesday.

The three Central Jersey districts — the 14th in Mercer and Middlesex counties; the 16th in Hunterdon and Somerset counties, Princeton and South Brunswick; and the 18th in Middlesex, where Democratic gubernatorial candidate Barbara Buono serves as state senator — are considered key battlegrounds where challengers have a rare shot at unseating incumbents.

the three districts have seen an infusion of cash from so-called 527-groups, which are organized under the federal tax code and are required to report names of contributors to the IRS but not the state Election Law Enforcement Commission, or ELEC.

The U.S. Supreme Court’s 2010 Citizens United ruling allowed political groups registered with the IRS to raise and spend unlimited amounts of money as long as the organizations remained separate and independent from the candidates they were supporting.

Four years ago, 527 groups spent about $14 million in the state’s gubernatorial and legislative elections, an amount that ELEC executive director Jeff Brindle called “significant at the time.”

But earlier this year, Brindle predicted these groups would spend about $25 million. An ELEC report expected to be released today shows that 527-group spending could be even more than he thought.

Unlike candidates and political committees, these groups do not have to report their contributions to the state, but they do have to report their spending to ELEC if they use what Brindle calls the “magic words” of “vote for” or “against” a candidate.

ELEC will ask state lawmakers to require full disclosure by groups who spend money in the state, he said.

In the 14th District, about $1.78 million has been spent on the re-election campaign of state Sen. Linda Greenstein and assemblymen Dan Benson and Wayne DeAngelo, all Democrats. Of that, $567,000 was spent by the Fund for Jobs, Growth & Security, a Democratic political action committee based in Washington, D.C. That total doesn’t include what Garden State Forward has spent.

About $441,000 has been spent on their Republican challengers — former state Sen. Peter Inverso and Assembly candidates Steve Cook and Ronald Haas.

In the 16th District, which is considered very competitive because of the balance between conservative Hunterdon County and the heavily Democratic townships of Princeton and South Brunswick, about $563,000 has been spent on the Republican incumbents, while at least $501,000 has been spent on the Democrats. the Democratic total doesn’t include the spending by Garden State Forward.

State Sen. Christopher “Kip” Bateman, a Republican, has been aided by $175,000 spent by the National Association of Realtors, a trade group based in Washington, D.C., and $40,900 spent by the New Jersey League of Conservation Voters.

Ed Potosnak, the group’s executive director and a one-time Democratic congressional candidate, said his group is spending most of its $55,000 budget on Bateman, with the rest going to two Democrats, Greenstein and Senate candidate Peter Barnes III in the 18th District.

The group’s mail ads are targeting Democratic and independent voters, touting the Republican senator as the state’s “greenest” lawmaker.

“We do more than issue paper endorsements,” Potasnak said. “We actually put muscle into elections to show that when you support the environment you will have our support when your election comes.”

Most of the political ads in the 16th District feature Assemblywoman Donna Simon and her Democratic challenger, Marie Corfield. Last year, Simon won her seat in a special election by less than 1,000 votes. the Fund for Jobs, Growth & Security has pumped at least $369,000 into this race, mostly for attack ads against Simon.

In the 18th District, at least $1 million has been spent on Barnes’ attempt to win Buono’s seat in the Senate, Assemblyman Patrick Diegnan’s re-election bid, and East Brunswick Councilwoman Nancy Pinkin’s bid for Barnes’ Assembly seat. that total doesn’t include spending by Garden State Forward.

For the Republican challengers — East Brunswick Mayor David Stahl and Assembly candidates Robert Bengivenga Jr. and Lisa Goldhamer — about $665,000 has been spent.