A Transport for NSW spokesperson said Illowra will remain in place with only minor adjustments of its boundaries taking place.

"The formal property acquisition process for the Nowra Bridge project started in August 2018," a spokesperson said.

"Transport for NSW is currently in negotiations with all affected landowners in line with recent NSW property acquisition reforms.

"The property at 125 Brinawarr Street is being acquired for the project. A portion of land is required at this location and the house will not be impacted or demolished.

"Minor adjustments to fencing, vegetation and the driveway will be required, and will be completed with consideration of heritage aspects of the property."

Illowra was built in around 1906 for Mark Fairles Morton, known for his contribution to the conservation of flora and fauna. Morton National Park was named after him.

He was elected to NSW State Parliament for the Shoalhaven in 1901 and, except for a three-year gap, represented the area until his death in 1938.

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When Mr Morton was first elected he received the largest vote ever recorded for one man in the Shoalhaven electorate.

Before his career in State Parliament he had served on the Nowra Municipal Council as a councillor and mayor. At one point he was also auctioneer with the then well-known firm Stewart and Morton.

His brother, Phillip H Morton, also held the seat of Shoalhaven from 1888 to 1889.

The house is just over an acre and features six bedrooms, four bathrooms, a swimming pool and a tennis court.

Illowra is believed to mean "good camping place, with plenty tucker" in an Aboriginal language.