It is the home of the 7th Earl of Rosse and his family, and as the castle is generally not open to the public,[2] though the grounds and gardens of the demesne are publicly accessible, and include a science museum and a café, a reflecting telescope which was the largest in the world for decades and a modern radio telescope.

[15] The Irish entry to the 2014 European Tree of the Year contest was the Birr Castle Grey Poplar (Populus × canescens).

[17] The demesne's charitable foundation offers quarterly, half-yearly and annual memberships, including unlimited visiting.

It was dismantled in 1914, but the structure was restored and the telescope reconstructed in the 1990s and is accessible to the public,[3] with occasional demonstrations of its movement, and talks.

[20] Trinity College Dublin leases land on the grounds of Birr Castle Demesne on which they operate the Rosse Observatory,[21] which includes the Irish station of the LOFAR network, known as I-LOFAR, as well as some other smaller radio telescopes.

These operations have brought astronomical research activity back to Birr after a century-long gap since the decommissioning of the Leviathan.

Astrophysicist Peter T. Gallagher, then of Trinity College Dublin, met Lord Rosse in 2010 while visiting the demesne in search of suitable quiet sites for radio-telescopy projects, and they agreed to repurpose an old sheep yard.

[22] The agreement led to the establishment of the Rosse Solar-Terrestrial Observatory, a Trinity College Dublin project, which was formally opened and blessed on 28 June 2014 (though already fully functional), with antennae picking up solar activity, even in cloudy weather.

The sheep pen building was converted into a control room, and a magnetometer, jointly operated between TCD and the Dublin Institute for Advanced Studies, was also installed.

In the meantime, the project team started work on establishing the I-LOFAR radio-telescope station (IE613), a node in a Europe-spanning network, which was largely built in 2016, and was switched on at Birr in 2017.

The I-LOFAR telescope, in 2018, observed for the first time a billion-year-old red-dwarf, flare star called CN Leo, almost 75 trillion kilometres away.