Mrs Jackson said she was leaving knowing the gallery was in great shape, having evolved into one of the country's leading regional art galleries under her directorship.
Visitor numbers had grown from 60,782 in 2011/2012 to 68,872 last year and the gallery had gone from a huge deficit to a small surplus.
"We effectively started with nothing and today we have built up the gallery's collection to 533 works, which I am immensely proud of."
Three of the past exhibitions Mrs Jackson helped curate are now touring.
That includes the Corrugations: The Art of Jeff Thomson exhibition named Best Exhibition under $20,000 at last year's NZ Museum Awards and Lynley Dodd: A Retrospective exhibition.
Mrs Jackson said Tauranga Art Gallery was the envy of many other city galleries around the country for its ability to secure important exhibitions others would like to exhibit such as the upcoming Wildlife Photographer of the Year exhibition from London's Natural History Museum. Tauranga will be the only venue in the country to run the exhibition.
Former Prime Minister Helen Clark, who officially opened the gallery in 2007, gave the gallery her stamp of approval when she and her family visited in 2013.
But while visitor numbers are going up, so are costs.
The gallery is run on a "tight budget" and its biggest costs were power, insurance and freight.
"With at least 16 exhibitions a year, I would hate to tell you how much our power bills cost. But I have to say in the last three years with the assistance of our audit chairman Gerald Gibbard we have managed to turn things around and achieved a small ($34,000) operating surplus."
Securing funding was a constant challenge and the gallery's share of ratepayer funded income was less than one per cent, which was not a lot compared with other galleries around the country, she said.
"Sometimes I felt like I was going to council with a begging bowl," she said.
The positive feedback from many visitors kept her going.
"It's been hugely satisfying to educate thousands of people about our art collections and exhibitions and to work closely with all the artists and our visitors. This is why I do what I do."
Until the gallery finds Ms Jackson's replacement an interim manager has been put in place and a business development manager started in December.
Ms Jackson said the time had come to stop talking about creating a museum for the city and just do it.
But having a combined art gallery and museum would not work, as the two institutions fulfilled different functions, she said.
Tauranga Art Gallery Trust trustee Debby Meldrum said Mrs Jackson's departure was a huge loss.
"For 11 years Penny has given exemplary service to the art gallery and to the city's ratepayers, and she has delivered some outstanding exhibitions to Tauranga. Penny is a pioneer in her field and she has also been very disciplined in her approach to managing the gallery's finances, which is exactly what you need in a gallery director."
