An Taisce has appealed the decision by Meath County Council to grant planning permission for 73 homes on part of the Slane Castle demesne.
The development is proposed by Pinebank Homes, Castletown, Navan, but this week the heritage organisation appealed the decision to An Bord Pleanála.
The scheme is earmarked for land on the Navan road in Slane that is opposite Slane Castle, and was sold by Lord Mount Charles two years ago.
An Taisce says it would be "contrary to the principles of sustainable development by promoting a development that is singularly designed for a car-dependent, commuter population".
There is a gamekeeper's cottage and a garden on the site, and they are both listed as protected structures in the 2001 Meath County Development Plan. The garden dates from the 1770s, while the cottage was built in the 1600s.
In the planning application the developer says the cottage will be repaired and restored to its original condition, and the garden wall will be repaired.
An Taisce says the development would "be seriously detrimental to the character and setting of the Kerry Garden and the singularly attractive and historic lodge".
The developers want to build detached, semi-detached and terraced homes, but An Taisce says it would fail to comply with the general development objectives for Slane village, which is on the busy Dublin-Derry road. It says the density of the houses is more than twice the recommended figure.
"This development, by virtue of its scale and design, neither respects the character of the existing village or the setting of historic structures."
It says any new development should be of low density, and be compatible with the character of the village.
It is also critical of Meath County Council, saying it did not have an archaeological assessment of the site carried out as recommend by Dúchas, the Heritage Service.
The appeal has been lodged on behalf of the Meath association of An Taisce by its planning officer Mr Kevin Mulligan. He said "the proposed development will impose a wholly inappropriate urban character on an environment that is deeply rural and sensitive in character".