Rhosyr was the site of one of the courts of the 13th-century Welsh prince Llewellyn the Great. Llys Rhosyr (Rhosyr Court) is now an important archaeological site, located close to Newborough. It was rediscovered and partially excavated in 1992, with local activists currently (2017) seeking funding to uncover the remaining two thirds.
Rhosyr elects a community council of fifteen councillors who, amongst other things, are responsible for maintenance of local footpaths and cemeteries. Until the 2012 Isle of Anglesey electoral boundary changes Rhosyr was also an electoral ward for the Isle of Anglesey County Council. However, since the 2013 local elections it has combined with neighbouring communities, Aberffraw and Bodorgan to form a larger ward, Bro Aberffraw, which elects two county councillors.
- "Rhosyr - Key stats (2011)". Retrieved 9 December 2017.
- "Bid to excavate the home of the last Princes of Gwynedd fails". Daily Post. North Wales. 1 May 2017. Retrieved 9 December 2017.
- "Rhosyr - Cyngor Cymyned/Community Council". Rhosyr Community Council. Retrieved 9 December 2017.
- "Isle of Anglesey (Electoral Arrangements) Order 2012" (PDF). legislation.gov.uk. The National Archives. Retrieved 9 December 2017.