About 70 people are involved in filming scenes for the first two episodes of the series, which is provisionally called Kingdom after his character Peter Kingdom.
An ITV drama spokesman said Mr Fry has been taking part in this week's filming, which is centred on Oakleigh House beside Swaffham College and the Greyhound pub, both in the Market Place.
Privately-owned Oakleigh House is the solicitor's home and office in the series, set in the fictional town of Market Shipborough, and the Greyhound gets re-named The Startled Duck pub for the drama's purposes.
Other cast members involved in this week's filming include Celia Imrie, as Gloria Millington, the solicitor's faithful receptionist and confidante, and Tony Slattery, starring as a cantankerous individual Mr Snell, who is always seeking litigation.
The spokesman said: "The cast usually stay in hotels or rent houses, cottages and flats in the area where filming is taking place, especially if it involves a long shoot like this, over 12 weeks.
"Quite a lot of the film crew are from the area, but those who come from London will also be staying in the area – so the local hotels, restaurants and cafés should be doing well over this period."
In later scenes to be filmed in Swaffham, St Peter and St Paul's Church, the Methodist Church, the library, the police station and a local jewellery shop will feature. Filming will also be taking place on location at Holkham and Hunstanton.
This week, scenes have been shot both inside and outside Oakleigh House and the Greyhound, which have been dressed for the part.
Joann Briscoe, who helps landlord Nicky George run the Greyhound, said the filming is taking place during the pub's closed hours so that normal trade is not affected.
"I think it's going to be great for the Greyhound. It's always been famous locally and now it will be famous nationwide on prime-time TV," she said.
A well-known actress appearing in later scenes will be Hermione Norris, of Cold Feet and The Kindness of Strangers fame. She plays the solicitor's troubled and lustful younger sister, Beatrice, who creates havoc when she comes to live with him.
Mr Fry's passion for this part of Norfolk was a major reason for him playing Peter Kingdom. He has a home in West Bilney and likes to return to the area as much as possible.