High street, Ynysddu
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 language 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" 
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.
- 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 on 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