Nils and Jan Anderson adopted a young dog from what is now the Animal Humane Society nearly a half-century ago. They were so smitten with their new pup, Molly, that they knocked on neighbors’ doors in the spring of 1974 and raised just shy of $200 for the nonprofit that brought them together.

The Plymouth couple turned it into an annual ritual, raising money each year for the Humane Society’s “Walk for Animals.” This year, they collected more than $78,000 — enough to push them over their $1 million lifetime fundraising goal after 45 years of door knocking, phone calls and letter writing.

“We just felt we had to give back,” said Jan Anderson, 81.

“It’s evolved. Each year, we walk a little farther and a little bit farther,” said her husband Nils, 77.

The Andersons are the humane society’s most successful volunteer fundraisers ever, said Molly Tlas, the organization’s major gifts officer. The couple enjoyed a bit of the royal treatment Saturday at the Walk for Animals, being chauffeured in a golf cart during the event.

“Jan and Nils have just stuck with it for 45 years. That’s really unheard of. It’s absolutely amazing,” Tlas said. “Their passion for animals has been their life’s work.”

The Animal Humane Society finds new homes for 23,000 orphaned and surrendered animals each year. In addition, it offers veterinary care and animal training, and conducts investigations into animal cruelty and neglect.

The organization dates back to 1878 but officially became the metrowide Animal Humane Society in 2007 when three similar nonprofits merged.

The Andersons, originally from the East Coast, moved to Minnesota in the early 1970s so Nils could take a job in food ingredient sales. They both grew up with animals, so they stopped at the humane society and found Molly. They’ve also adopted dozens of cats in the years since.

The couple have no children, so their pets — and their fundraising on behalf of animals — have been their passion.

“We just believe in what we are doing,” Nils said, pointing out that the Animal Humane Society is a local nonprofit that relies solely on donations and nominal fees for adoptions and services.

Jan said she’s always touched when she meets others who share their love for animals. She recalls ringing a doorbell once and finding a mom who called to her children, “Animal Humane Society!”

“All the kids ran down with their piggy banks and money,” Jan said.

The couple has kept track of donors who have come to expect their calls and visits each spring. They’ve set up a fundraising website and a Facebook page to keep up with the times.

But in the end they believe their success and longevity are tied to the personal connections they’ve made with donors.

“The personal touch is still the best,” Nils Anderson said.