After the first week of free agency last month, a sports betting site lowered the odds of the Vikings winning the Super Bowl from 75-1 to 66-1.

Hey, at least that’s some progress.

The Vikings are hardly a threat to win the big game next season, but they seem to be making strides. After a 5-10-1 record that led to the firing of coach Leslie Frazier, in has come Mike Zimmer.

Zimmer, a head coach for the first time, had been an NFL defensive coordinator for the previous 14 seasons, and he obviously knew Minnesota needed significant help on that side of the ball. So that has been the main thrust in free agency.

Of the seven players the Vikings have signed who played elsewhere last season, six are defenders. Heading the list are defensive tackle Linval Joseph, cornerback Captain Munnerlyn and defensive end Corey Wootton.

“I think they positioned themselves well because obviously it was critical to rebuild that defense,” said CBS analyst Rich Gannon, a former Vikings quarterback.

The Vikings ranked 31st in the NFL in total defense last season and 32nd and last in points allowed. Wanting to get younger, they watched as defensive end Jared Allen, 32, left for Chicago, and they probably won’t re-sign defensive tackle Kevin Williams, 33.

The other defensive free agents to have signed are defensive tackle Tom Johnson, cornerback Derek Cox and linebacker Jasper Brinkley, who played for the Vikings from 2009-13. The key re-signing was defensive end Everson Griffen, 26, who got a five-year, $42 million deal to replace Allen as a starter.

On offense, the only new player the Vikings have brought in so far has been guard Vlad Ducasse, who likely will be a backup. They are expected to return all 11 offensive starters from last season, including quarterback Matt Cassel, who was re-signed to a two-year, $10 million deal.

Minnesota’s quarterback problems last season were well chronicled. But at least Cassel provided some optimism when he went 3-3 as a starter to close the season, including passing for 382 yards in a 48-30 December upset of Philadelphia.

“The quarterback situation is still a question mark,” Gannon said. “But they have a new offensive coordinator with Norv (Turner), who has had a lot of success with quarterbacks, and you re-signed Cassel at a good price. And at least they haven’t given up completely on (Christian) Ponder, which I think is important because he’s still a young, developing player.”

Ponder steered the Vikings to a 10-6 mark and a playoff berth in 2012 before struggling last season as the primary starter. It remains to be seen if he will be on the roster when the season opens.

Overall, offense wasn’t a huge problem. Minnesota, getting 1,266 yards rushing from Adrian Peterson, ranked 13th in yards gained and 14th in points scored.

The Vikings can’t do everything at once. So while they did re-sign wide receiver Jerome Simpson and guard Charlie Johnson, most of the offseason work has been to shore up the defense.

“I think, when you look at the offense, they did get to the playoffs two years ago (with a similar cast), although Ponder had played better for them,” said NFL Network analyst and longtime NFL executive Charley Casserly. “On defense, they’re better on paper than last year. Mike’s going to build a better defense going forward.”

The top outside signing was Joseph, who got a five-year, $32.5 million deal after playing his first four NFL seasons with the New York Giants. Joseph, 25, provides the rugged sort of nose tackle the Vikings haven’t had since Pat Williams retired after the 2010 season.

“I like Joseph,” Casserly said. “He was probably the highest-rated young defensive tackle that came out (in free agency). He’s the guy you want to sign because he’s entering his prime. And Wootton is a strong player against the run.”

Wootton, who signed a one-year, $1.5 million deal after playing his first four NFL seasons with Chicago, probably won’t start. But he should get plenty of snaps rotating with holdover defensive end Brian Robison and Griffen.

There also could be a three-man rotation at defensive tackle with Joseph and Johnson joining holdover Sharrif Floyd. Put it all together, and Robison is pleased with how the defensive line has been beefed up.

“I really like the moves,” he said. “I think we’ve brought in some good players. I’m really excited about next year.”

Safety Harrison Smith likes the moves the Vikings made in the secondary after a season in which they ranked 31st in passing yards allowed. The 5-foot-8 Munnerlyn, who has returned four interceptions for touchdowns the past two years, figures to replace the departed Chris Cook as a starter, and Cox will help provide depth.

“I’m excited about those guys as playmakers,” Smith said.

The biggest concern that remains for Minnesota on defense, if not the entire team, is at linebacker. Brinkley will compete for the starting job in the middle with Audie Cole, but he’s not a guarantee to even make the roster after a mediocre season with Arizona.

Erin Henderson, a starter the past three seasons both inside and outside, was released in February not long after his second arrest in a 1-1/2-month span on suspicion of DWI.

Chad Greenway, after making two straight Pro Bowls, had an off year in 2013 while playing with a broken bone in his wrist and recently agreed to a $1 million pay cut for 2014.

“Greenway is a proven player, but I think the middle and the outside are questionable,” Casserly said.

But there is still plenty of time for the Vikings to address needs, either in free agency or through the draft in May. Minnesota has $11.07 million left in salary-cap room, although about half of that will go to draft choices.

Nobody is realistically thinking of a Super Bowl win for the Vikings, as evidenced by the still-long 66-to-1 odds oddsmaking site Bovada.com has established. But making the playoffs might not necessarily be a crazy proposition.

“I think they’ve done enough so far to have a chance (at the postseason),” Gannon said. “I think the team lost confidence last year with the quarterback situation. So it will come down to the quarterback and how much they’ve been able to improve the defense.”

Follow Chris Tomasson at twitter.com/christomasson.

NEW GUYS IN TOWN

A look at the seven players the Vikings have signed in free agency:

JASPER BRINKLEY

Position: Middle linebacker

Age: 28

Years pro: 5

Last team: Arizona Cardinals

Outlook: Brinkley, returning after playing with Minnesota from 2009-12, will battle Audie Cole for a starting job. After starting 15 Vikings games in 2012, he got a two-year deal from Arizona. But he was waived after starting just three games in his one season there. Brinkley will try to help a mediocre linebacking corps.

DEREK COX

Position: Cornerback

Age: 27

Years pro: 5

Last team: San Diego Chargers

Outlook: In his only Chargers season, was ranked 104th by Pro Football Focus in 2013 out of 110 NFL cornerbacks. Cox will try to bounce back after he had been reasonably effective in his first four seasons with Jacksonville. He isn’t expected to start, as Minnesota’s top cornerbacks are Xavier Rhodes and Munnerlyn.

VLAD DUCASSE

Position: Guard

Age: 26

Years pro: 4

Last team: New York Jets

Outlook: An underachiever after being a second-round pick in 2010. While starting four games in 2013 at left guard, Ducasse was ranked 56th out of 81 guards by Pro Football Focus. The Vikings are hoping he can boost his career in a lower-pressure situation. With Charlie Johnson having been re-signed, he won’t be expected to start.

TOM JOHNSON

Position: Defensive tackle

Age: 29

Years pro: 3

Last team: New Orleans Saints

Outlook: The 6-3, 288-pound Johnson never has started an NFL game, but he intrigues the Vikings. He expects to fit better in a 4-3 than with the Saints, who often used just three down linemen. Johnson could be in a three-man defensive tackle rotation. His one-year deal is for $850,000 but has $600,000 in incentives.

LINVAL JOSEPH

Postion: Defensive tackle

Age: 25

Years pro: 4

Last team: New York Giants

Outlook: The 6-foot-4, 328-pound Joseph provides the Vikings with a rugged nose tackle they haven’t had since Pat Williams retired after the 2010 season. He should step right into the starting lineup. Joseph was a starter on a Giants team that won the Super Bowl three years ago. Now, his career could be ready to really take off.

CAPTAIN MUNNERLYN

Position: Cornerback

Age: 25

Years pro: 5

Last team: Carolina Panthers

Outlook: He’s undersized at 5-8 but makes up for it with his feistiness. Has returned four interceptions for touchdowns the past two years and five over the past four seasons. Figures to move in as a starter in place of Chris Cook, who didn’t have an interception in four seasons.

COREY WOOTTON

Position: Defensive end

Age: 26

Years pro: 4

Last team: Chicago Bears

Outlook: Figures to come off the bench as the Vikings rotate defensive ends. Wootton’s agent, Mike McCartney, said Wootton would have no problem with that role and pointed out he had his best season in 2012, when he had seven sacks while starting just seven games. Wootton is coming off hip surgery in January.