There is evidence of human occupation of this site from Neolithic times.
Excavations in the 1960s at the site of the current Industrial Estate uncovered two large henge monuments and a series of hengiform pit circles from the late Neolithic period. Excavations in 2006 and 2007 at the Bryn Cegin site (extending the industrial estate) found an early Neolithic house and later, possibly Romano-British, settlement
In 1648 during the English Civil War the Battle of Llandygai was fought at Y Dalar Hir, near Llandygai. Royalist forces of 150 horse and 120 foot soldiers led by Sir John Owen engaged Parliamentarian forces led by Colonel Carter and Colonel George Twistleton.
The village of Llandygai is recorded at the beginning of the nineteenth century as consisting of eight or nine houses. The village was later developed by quarry ownber Edward Gordon Douglas-Pennant, 1st Baron Penrhyn of Llandygai as a ‘model village’ for his estate workers, in which ‘no corrupting alehouse’ was permitted. It lies immediately outside of the walls of the Penrhyn Castle demesne walls, with the entrance to the village being some 100m from the castle's Grand Lodge.
This model village was mostly constructed in the 1840s in a ‘vernacular revival’ style which conformed to the Picturesque ideal. The model village was built within the loop of the road to Conwy from where it branched off Telford’s newly built Holyhead to London road. Each house was built in a similar style but none was to be identical. They were furnished with ample gardens and the layout was such that no house’s front door faced another.
Llandygai Church 
The present church dates to around 1330 and was much restored and extended by the diocesan architect, Henry Kennedy, in 1853. The church is of cruciform structure with a central tower. It is a Grade II* listed building.
The church has six bells. The bells naturally sound very loud inside the ringing chamber (from where the bells are rung); to combat this the bells are permanently fitted with leather muffles on both sides of the clapper. When ringing the bells they have a strange sound because of this; almost as if they are ringing inside a large tank of water.
In the church is a marble monument to Archbishop John Williams, the Lord Keeper of the Great Seal during the reign of James I. There is also monument by Richard Westmacott to the first Lord Penrhyn, in which the sarcophagus is flanked by a quarryman and peasant woman, described by Eric Hobsbawm as “the earliest sculpted proletarians”.
There are accounts of schooling for twelve children under the Welsh Trust in the late seventeenth century, and later a circulating school established in the area in 1750. Shortly after her husband’s death, the first Lady Penrhyn set up a school for girls in the village in what is now Neuadd Talgai. A school for boys was built in 1843.
The village today 
The model village, within the loop of the former line of the A55 road, retains much of its original character, despite some more recent additions, having been declared a conservation area in 1974. The village is next to the Grand Lodge affording the principal entrance to Penrhyn Castle, the former seat of the Penrhyn family, now a National Trust property open to the public.
Outside the model village are also to be found –
- Off the A5 towards Bangor:
- Off the A5 towards Bethesda:
- Parc Cegin business park (in development)
- Off the former line of the A5, now a narrow lane:
The village name has been spelt also as Llandegai. The correct Welsh spelling is Llandygái, the accent signifying that the last syllable is stressed as opposed to the last-but-one, the usual pattern. All forms are in use today with Llandygai the most commonly accepted.
- www.geograph.co.uk : photos of Llandygai and surrounding area
- Archaeology at Parc Bryn Cegin
- Village School
- Llandygai Church
- Joshua Pollard (2001) The Neolithic in Prys Morgan (ed.) The Tempus History of Wales 25,000 BC – AD 2000, Tempus ISBN 0-7524-1983-8
- Frances Lynch (1995) A Guide to Ancient and Historic Wales: Gwynedd, CADW ISBN 1-85760-197-1
- Heneb. "Archaeology at Parc Bryn Cegin". Retrieved 27 June 2009.
- A.H. Dodd (1968) A History of Caernarvonshire , Caernarvonshire Historical Society/Bridge Books ISBN 1-872424-07-4
- Parry's Railway E&W Publishers 1970 ISBN 0-85104-013-6
- Edmund Hyde Hall (1811) A Description of Caernarvonshire (1809-1811) Caernarvonshire Historical Society, 1952
- Gwynedd Council (2006). "Llandygai Conservation Area Character Appraisal". Retrieved 27 June 2009.
- T. D. Breverton, The Book of Welsh Saints (Cyhoeddiadau Glyndŵr, 2001)
- Ysgol Llandygai. "Eglwys Sant Tegai, Llandygai". Retrieved 27 June 2009.>
- Church in Wales. "St. Tegai". Retrieved 27 June 2009.
- "St. Tegai’s Church". Photos of Churches. Retrieved 27 June 2009.
- David Gwyn (2006) Gwynedd: Inheriting a Revolution: The Archaeology of Industrialisation in North-West Wales Phillimore
- "Ysgol Llandygai". Retrieved 27 June 2009.
- Gwynedd Council (2007). "Llandegai Gypsy Site update". Retrieved 27 June 2009.
- North Wales Probation Area. "Approved Premises". Retrieved 27 June 2009.
- "Bangor Cricket Club". Retrieved 27 June 2009.