Democrats have also improved their position in Colorado and Arizona compared to this point in 2012, according to a CNN analysis of the latest early voting numbers.
Republicans, meanwhile, appear to be in a slightly better position in Iowa and North Carolina -- where the electorate includes more whites at this stage than it did at the same point in 2012.
These findings represent absentee ballots and early votes cast by more than 12.6 million Americans across 37 states where data are available. CNN has partnered with Catalist, a data company that works with progressive candidates and groups, to receive detailed early vote return information this year. Catalist's voter list connects returned ballots with demographic and registration information, such as party registration, gender and age, and allows a closer look at who has already cast a vote.
These are not results -- ballots aren't tallied until Election Day. But the findings provide clues on who is voting, and which party is turning out to vote. And while the numbers track voters' party affiliations, not all Democrats are voting for Clinton, and not all Republicans are supporting Donald Trump.
Here's a look at the early voting data from several battleground states:
Registered Republicans are leading in returned ballots by about 11,500 -- a 1.7 percentage-point-edge over Democrats out of 682,000 votes cast so far. But that's well off the 8.5-point advantage the GOP had at this stage of the 2012 race.
Two-thirds of Arizona voters cast their ballots before Election Day in 2012 -- making these early voting numbers crucial to watch for Clinton and Trump.
The election is fully underway in Colorado, which conducts its elections almost entirely by mail. So far, 422,677 Coloradans have voted, and things are looking good for Clinton.
Democrats are ahead of Republicans in terms of returning ballots, and their lead is growing. Their advantage doubled this week, from about 10,000 to almost 24,000. And that's not the only bad news for Republicans: At this point four years ago, the GOP actually had a lead of more than 6,000.
The Republican advantage in Florida may be slipping away as Democrats turn out to vote early.
Now that in-person early voting is underway, the GOP advantage has been slashed by about two-thirds. They were up by about 18,000 votes earlier this week, but now they lead by only about 6,000 -- or 0.3 percentage points. While they are still leading, they are far behind the advantage of 6.8 points -- almost 73,000 votes -- that they had at this point in 2008.
In more possible good news for Clinton, there are signs that Hispanic turnout has swelled in the Sunshine State. So far this year, about 13% of early voters are Hispanic, up from about 8% at this point in 2008.
We don't have comparable data from Florida for 2012, which was a closer race than in 2008.
In each of the two previous presidential races, more than half of Florida's electorate voted early. The early vote share was 56% in 2012, and that number is expected to continue climbing in 2016.
Almost 827,000 votes have already been cast in Georgia, a 39% increase from this point in 2012 -- when half the state voted early.
The Peach State doesn't register voters by party, so it's impossible to know whether more Democrats or Republicans have voted.
But if Clinton is going to pull off the upset here, she'll need strong turnout from African Americans -- and there are signs that their share of the vote has dropped a bit from where it was at this point in 2012. Black voters made up 34% of Georgia's early voting population at this stage of the 2012 race, compared to 30% this year.
Iowa, where 43% of the vote came early in 2012, continues to be Trump's strongest state in terms of early voting.
Registered Democrats still have an advantage over Republicans, to the tune of about 40,000 votes, or 12.6 percentage points out of nearly 340,000 ballots cast.
But at this point in 2012, Democrats led by more than 55,000 votes, or 14.9 points. They'll need to close that gap if they want to hold onto the state that Barack Obama carried twice.
Overall turnout is down for both Democrats and Republicans this year in Iowa. At this point in 2012, nearly 419,000 ballots had been cast.
Democrats have benefited greatly from early voting in Nevada, which began last weekend. They now lead Republicans by almost 23,000 votes, or 11.3 percentage points -- which is slightly ahead of their 2012 edge of 10 points at this stage.
Republicans had small leads earlier this month, when voters were casting absentee ballots.
But in-person turnout has been strong in Democratic-heavy Clark County, which includes Las Vegas.
Nevada is a crucial early voting state. In 2012, 69% of the state's electorate cast their ballots before Election Day.
Democrats have built a large lead ahead of Republicans in North Carolina, and their lead has grown in recent days are voters hit the polls early. Right now, they lead the GOP by about 149,000 votes, or 18.4 percentage points of the state's nearly 812,000 votes cast.
However, for the first time since in-person early voting started last week, Democrats are behind their 2012 pace. At this point four years ago, they led Republicans by 167,401, or 20.5 points, in the early vote. And even with that advantage, it wasn't enough for Obama to win the Tar Heel State against Mitt Romney.
North Carolina reduced its early voting window, but the total ballots cast so far are largely on track with 2012 -- when 61% of the vote was cast early.
If Clinton wants to flip North Carolina blue this year, she'll need strong turnout from African-Americans. At this point in 2012, black voters were 30% of the electorate. They're only about 24% today. Meanwhile, the share of white voters has climbed from 64% at this point in 2012 to 72% now.
Almost 680,000 people have already voted in the battleground state of Ohio.
That's about 18% down from the turnout levels in 2012. After the last presidential election, Ohio's Republican-controlled legislature slashed back the number of early voting days. There are some signs that the drop-off has been heavier in Democratic-leaning counties, bad news for Clinton.