The Knockoneil River (sometimes spelled Knockoneill), is a small to medium sized river in Northern Ireland located near Maghera. It starts on Carntogher Mountain then flows eastwards towards Swatragh. Knockoneil is a townland in the rural area of Slaughtneil and is the townland the rivers named after. The Knockoneil starts its course and its a similar width to the Grillagh River. The river widens as it passes through Swatragh and onwards to Upperlands where a lot of hydro energy from the river is used for Clarke's mill onwards through Upperlands.The river flows quite swiftly through the village of Upperlands passing under Upperlands and Boyne Bridges as well as the Old Mills. From Upperlands it quiets down through the Countryside outside Upperlands and on to Culnady where it flows under Dunglady Bridge an old bridge near Culnady named after Dunglady Fort which its name means Fort Above The Clady. Shortly downstream it merges outside Culnady with the Grillagh River to form whats known as the Clady River.

Knockoneil River Means Nialls Hill River.

The River is famously known to be the reason William Clark & Sons in Upperlands exists as being the main power source for the Mill. The river is diverted through massive sluice gates downstream from Amportane Bridge this tailrace feeds five manmade lakes known locally as The Dams the river was used to power the mill and its electricals as well as the dyeing process this caused dye pollution on the river. The river was similar to the Grillagh being many flax mills were built along the river most well known being Lagans Scutching Mill in-between Swatragh and Upperlands.

The River is leases by the Clady And District Angling Club funded in 1962.

Tammybrack Bridge, Corlacky Hill Bridge, Knockoneil Bridge / Upper River.

Swatragh Bridge, Beagh Bridge, Amportane Bridge / Middle River.

Upperlands Bridge, Boyne Bridge, Dunglady Bridge / Lower River.

Green Water Burn Starts south of Brockaghboy windfarm and flows a few miles and into the Knockoneil

Corlacky Burn Starts on the Corlacky hill and flows into the Knockoneil.

Craigavole Burn The Craigavole burn is the third largest tributary of the Knockoneil river it starts in Craigavole townland and flows east of Swatragh underneath the GAC Swatragh football pitch and rounds a circle east of the town and then straight south and flows into the Knockoneil north of Beagh Bridge.

• http://www.wmclark.co.uk/
• https://www.yumpu.com/en/document/view/50861608/upperlands-institute-of-environmental-management-and-assessment
• https://apps.spatialni.gov.uk/PRONIApplication/
• https://visionsofthepastblog.com/2019/12/14/knockoneill-court-tomb-derry-ireland/
• https://www.bbc.co.uk/news/uk-northern-ireland-39096665#:~:text=world's%20oldest%20companies.-,William%20Clark%20and%20Sons%2C%20based%20at%20Upperlands%2C%20outside%20Maghera%2C,the%20business%20is%20still%20intact.
• http://www.wmclark.co.uk/flax-visitor-centre-grand-opening/
• http://www.wmclark.co.uk/progress-perseverance-tale-upperlands-alex/