Old Lyme — Jeffrey Andersen, who over the last four decades has turned the Florence Griswold Museum into a "major regional art museum," is retiring as its director.

The museum announced the move to members on Monday and to the media on Tuesday.

In a news release, Andersen said, “It has been one of the greatest privileges of my life to be a part of this Museum,” and in a phone interview, he expanded on that and spoke about the camaraderie among all the people involved with the museum.

Andersen, 63, said, “It was a hard decision ... but I think it’s a good time (to step down). We have these exciting plans in the future, and I would have to really make a pretty long-term commitment (of five to seven years).”

Those plans include expanding the museum’s gallery space by adding a new wing to the Krieble Gallery; updating the Marshfield House to provide more space for people to gather for events such as lectures and educational programs; making the research center, library and archives more publicly accessible, and unifying with a landscape plan the various parcels of the original Florence Griswold property that the museum has acquired.

“They’re really solid visions, but they’re going to take several years to realize. I’m at a point in my life ... I just felt like, while I’ve been thrilled to be part of the planning and the thinking and the conceptualization (of those projects), the actual implementation would be a wonderful opportunity for the next director to really sink their teeth into and take the institution in these ways,” Andersen said.

He will remain at the museum until a new director is on board. There will be a national search, and Ted Hamilton, the president of the Flo Gris board of trustees, said the hope is to hire a successor by the end of the year.

Hamilton had nothing but praise for Andersen, saying, “He got there when Florence Griswold was really an old historic house with a few paintings. And now it’s a really major regional art museum. ... He’s done a tremendous amount.”

The Flo Gris was a volunteer-run organization when Andersen was hired in September 1976 to be its director and only employee.

Andersen, who grew up in the San Francisco Bay area, had just earned his master’s degree in museum studies from Cooperstown Graduate Program in Cooperstown, N.Y. A dean at the school told him about the Flo Gris job because it was about the intersection between art and history, something that was and is a great interest of Andersen’s.

The Old Lyme locale is where, back in the early 1900s, artists flocked to Florence Griswold’s boarding house. They painted there during the summer, with the site becoming the home of the Lyme Art Colony and of American impressionism.

The Florence Griswold Museum thrived under Andersen’s leadership. What was once a site that attracted fewer than 1,000 visitors annually now draws almost 80,000. The museum boasts more than 20 staff members, 3,000 members and 225 volunteers. The Florence Griswold House was designated a National Historic Landmark in 1993.

Last year, the New England Museum Association honored Andersen with its Lifetime Achievement Award.

There were certainly significant moments in his years at the museum, but Andersen said, “I think what I’m most proud of is the daily vitality that I feel when you walk round the place and you interact with a volunteer or a visitor, and you see the kind of pleasure people take. You know, having lunch at Café Flo and seeing our current exhibition — just the rhythm of that is something that is kind of magical to me.”

He talked, too, about the relationships he’s developed and said, “We have a remarkable group of people (at the museum) who are just absolutely so talented and so devoted.”

He added, “I’m an operations kind of guy who loves to be in the trenches, working with both staff and volunteers on projects. I know I’m going to miss that terribly.”

Andersen said he’s excited for the future of the museum and also for his chance to have a little more freedom to travel with his wife and to spend more time with his family in California. He and his wife — Maureen McCabe, an artist who was a professor at Connecticut College in New London for many years — live in Quaker Hill.

Andersen does intend to stay active in the arts, including working on projects, giving talks and writing.

The accomplishments of Andersen and his team over the years have been many and varied.

Andersen helped create an endowment fund, and that fund now provides one-third of the museum’s annual operating budget of $2.6 million.

Andersen, along with trustees and professional colleagues, worked to reacquire the original Florence Griswold property for the museum. It took seven transactions, ending with the purchase of the final parcel last year.

Andersen, on behalf of the Flo Gris, helped The Hartford Steam Boiler Inspection and Insurance Co. assemble a collection of 190 paintings and sculptures by American artists associated with Connecticut. Hartford Steam Boiler donated the entire collection to the Flo Gris in 2001.

The Flo Gris rebuilt historic gardens, relocated the William Chadwick artist studio, constructed education and landscape centers, and opened the Robert and Nancy Krieble Gallery. Those were the results of capital campaigns that, in total, raised more than $20 million.

Hamilton said that Andersen is “the type of person who is involved in everything and rolls up his sleeves and works.” He added that Andersen is at the museum seven days a week and is well-liked by all the people who work at the Flo Gris as well as people in the community.

Asked what Andersen has meant to the museum, Hamilton said, “He’s meant everything to the museum.”

k.dorsey@theday.com