Meanwhile, Democrats also surpassed —- albeit slightly —- Republicans in returning vote-by-mail ballots, an area that in the past has been a hallmark of GOP get-out-the-vote efforts in Florida.
A final count of registered voters for the general election is due by the end of October, said Meredith Beatrice, a spokeswoman for the Florida Department of State, which includes the Division of Elections. The registration deadline is 5 p.m. Tuesday.
The monthly voter-registration report for September showed Democrats had a net increase of 67,546 registered voters during the month, pushing their overall number of registered voters to 4,800,905.
In the same time, Republicans added 41,873, putting their registered-voter count at 4,500,960.
Meanwhile, people declining to check membership in any political party while registering grew by 63,242 in September. There are now 3,012,910 registered independents in Florida.
Democrats currently make up just under 38 percent of Florida's registered voters. Republicans account for slightly more than 35.5 percent, while independents are about 24 percent.
Four years ago, those percentages were 40 percent for Democrats, 35 percent for Republicans, and 21 percent for independents.
Minor-party voters collectively grew by 3,341 in September, to 340,511, making up more than 2 percent of the overall registered voters.
Republicans have pointed to a long-term closing of the registration gap with the Democratic Party, which has traditionally outnumbered the GOP.
University of Florida political-science professor Daniel Smith, who specializes in voter-registration issues, said the closing of the gap during the past few years is more of a reflection of voters being removed from the election rolls, which can be due to inactivity, death, leaving the state or even changing affiliations.
Since January 2013, approximately 515,000 Democrats and 436,000 Republicans have been taken off the voter rolls. Meanwhile, Smith noted that in the same time Democrats have registered 80,000 more new voters than the GOP.
Also, Smith noted that of the various methods for people to register to vote, third-party groups —- mostly progressive advocacy groups —- accounted for 40 percent of the new registrations in the state's September report.
"These groups cannot say you have to register with one party or another, but we know at the operational level that it's less likely to be Republican and more likely to be no-party voting and Democrat," Smith said.
The registration numbers come as more than 500,000 of the state's 12.66 million voters have already cast vote-by-mail ballots.
As of early Monday afternoon, Democrats had returned 210,734 of the ballots, Republicans 210,707.
Historically, Republicans have outpaced their Democratic counterparts in vote-by-mail, formerly known as absentee ballots, while early voting has tended to lean to the Democrats.
Of the 1.87 million vote-by-mail ballots cast in the 2014 general election, 44.4 percent were from Republicans and 37.6 percent from Democrats.
For this year's contest, independent voters have returned 77,289 ballots, and 14,359 have come back from people with minor parties.
Another 2.4 million vote-by-mail ballots that have been sent out by county supervisors of election have yet to be returned. Of those ballots, 981,771 have gone out to Republicans, 941,157 to Democrats, 446,413 to independents and 58,105 to minor party voters.
More Floridians registered as Democrats or independents than as Republicans last month, the state Division of Elections reported Monday with a day remaining to sign up to vote in the Nov. 8 elections.