Llanfyllin (Welsh pronunciation: [ɬanˈvəɬɪn] – audioⓘ) is a market town and community in Powys, Wales.

The community (which measures 41.8 square kilometres) population in 2021 was 1,586 and the town's name means church or parish (llan) of St Myllin ('m' frequently mutates to 'f' in Welsh).

[7][8][9][10] The medieval motte-and-bailey castle of Tomen yr Allt was probably destroyed by Llywelyn ap Gruffudd in 1257.

The charter was confirmed by Edward de Charlton, Lord of Powys under Henry V.[2][13] Llanfyllin Town Hall, which dated from 1789,[14] and served as the meeting place of the borough council, was demolished in 1960.

The present building which dates to around 1706 is mainly of locally-made red brick with battlements and a Welsh slate roof.

[21] It is likely that a house was built on the site after the destruction in 1257 of Tomen yr Allt, a motte-and-bailey castle which stood on one of the hills above it.

In 1945 the estate was broken up; most of the land was bought by its tenant farmers, and the hall and 33 acres were sold to one buyer to become an hotel.

[21][22] The grounds of the hall are listed at Grade II on the Cadw/ICOMOS Register of Parks and Gardens of Special Historic Interest in Wales.

[25][26] This old Victorian building had stood empty since the mid-1980s until a local voluntary group, the Llanfyllin Workhouse Project, started to renovate it for community use.

The 2009 inspection of the high school reported GCSE examination results as well above the local and national average.

The main bus service is the number 76 to Welshpool operated by Tanat which runs Monday to Saturday.

[39] The Lonely Tree of Llanfyllin was a large Scots pine in an isolated position on Green Hall Hill above the town (at 52°45′45″N 3°15′02″W / 52.7624°N 3.2506°W / 52.7624; -3.2506).

It featured in several local traditions: it was hugged for good fortune, marriages were proposed at the tree and cremation ashes were scattered beneath it.