|Ynysddu shown within Caerphilly|
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|Sovereign state||United Kingdom|
Ynysddu is a small village in the Sirhowy valley of south-east Wales. It is part of the district of Caerphilly within the historic boundaries of Monmouthshire. It is next to Cwmfelinfach, 4.3 miles (6.8 km) north of the town of Risca and 4 miles (5.1 km) south of the market town of Blackwood, about 10 minutes by road from the M4 motorway and 35 minutes from the Severn Bridge. The electorate in 2008 was 2,905, increasing to 3,948 at the 2011 Census.
Ynysddu was founded in the early 19th century by the enlightened local colliery owner John Hodder Moggridge, who lived at nearby Woodfield Park. It got its name from Ynsyddu Farm, which was built by Moggridge in 1804. Ynysddu comes from the Welsh descriptive words 'Ynys' ('island' or 'river meadow') and 'ddu' ('black'). 'Black river meadow' is appropriate for the landscape of the area.
After he became alarmed at the terrible living conditions of the poor in the 1820s Moggridge also built 'The Ranks'. Founded as a social experiment 'The Ranks', like similar properties in Blackwood, allowed a few workers to lease a plot of land to build a cottage and garden allotment. 'The Ranks' were situated near the Black Prince pub, but have long since disappeared.
In 1901 Kelly's Directory of Monmouthshire said:
"YNYSDDU is a hamlet of this parish, having a station on the Sirhowy section, London and North Western railway, 10¼ miles north-west from Newport. Here are Baptist and Calvinistic and Primitive Methodist chapels. Post Office.—John Hughes, sub-postmaster. Letters received through Newport at 8.55 a.m.; dispatched, 6.30 p.m. week days only. Postal orders are issued here, but not paid. Pontllanfraith is the nearest money order & Blackwood the nearest telegraph officeBoard School, erected in 1877, at a cost of £1,500, & erected in 1899, for 167 children; average attendance, 101; Thomas Harries Phillips, master; Miss Susanna Evans, assistant mistress. Railway Station, James Williams, station master" 
- See also Category:People from Ynysddu
- Welsh poet William Thomas (1832–1878). was born in Ynysddu, taking his bardic name Islwyn (meaning below the grove) from the parish of Mynyddislwyn, itself named after the mountain which towers over the village. His two best-known poems are both entitled "Yr Ystorm" ("The Storm"); one is a long philosophic poem over 9,000 lines long.
- Singer Ricky Valance (real name David Spencer) was born here.
- Scott Morgan, sports shooter, born 1990; Olympic Trap Shooting (Shotgun)
- Jackie Barnett, who lived in Ynysddu from the age of two, represented Wales at two Commonwealth Games and also played netball for Wales.
Ynysddu Primary School is located in the town; its headmaster as of 2009[update] was John Farmer.
Sport and leisure
Ynysddu Rugby Club is a member of the Welsh Rugby Union and is a feeder club for the Newport Gwent Dragons. The first Ynysddu game recorded was in 1894 against Abercarn, and was played in the church field at Mynyddislwyn. Ynysddu originally played in an all-black strip, but now play in Black and Red.
Ynysddu Crusaders Football Club was relaunched in 2008 (having originally existed from 1915–1939), following the formal amalgamation of Ynysddu Welfare Crusaders AFC (formerly Ynysddu Welfare AFC 1947–2006) and Crusaders [Seniors] AFC (2003–2008), the latter having superseded Cwmfelinfach Colts AFC (1978–2003). They are affiliated to the Gwent County Football Association and are members of the Welsh Autoparts Gwent County FA League and the Ryan Transport Ltd North Gwent Football League. Club Colours are gold and black. They play their home games at Nine Mile Point Miners' Welfare Grounds, Graig View, Ynysddu, with their headquarters at The Ynysddu Progressive Club in Commercial Street.
Nearby is the Sirhowy Valley Country Park. The Ynys Hywel Activity Centre, located there, offers adventure activities such as abseiling, canoeing, mountain biking, rock climbing, orienteering and hill-walking.
The Ynysddu Hotel is also located in the village.
- "Community population 2011". Retrieved 8 November 2011.
- Caerphilly existing electoral arrangements
- Moggridge, a vocal opponent of the truck system, founded the model workers' town Blackwood. He was the son of John Moggridge (died 1803), a wealthy clothier of Bradford-upon-Avon; he married Sarah, daughter of M. Jeffreys, of Blakebrook, Worcester. He lived at Llanrumney Hall in 1812–23
- A Pocket Guide to the Place-names of Wales : Hywel Wyn Owen :Publisher: University of Wales Press : ISBN 978-0-7083-1458-6
- Wild Britain: Welsh place names
- Kelly's Directory of Monmouthshire
- "Storm, Y" Gyntaf gan Islwyn : Meurig Walters ISBN 978-0-7083-0754-0
- Oakdale village
- Monmouthshire Writers. A Literary History And Anthology : W.J.Townsend ("Dromio") Collins : Publisher: R.H.Johns Ltd. ISBN B001G6J3ZK