- 1652 400 people die of plague in Haverfordwest, the last occurence of plague in Wales.
- 1722-23 Smallpox kills 71 people in Carmathen and about 50 in Holyhead.
- 1727-1731 Hundreds die of typhus.
- 1785 Prior to the building of the Bridge, ferries across the Menai Straits often capsized. In this year a ferry carrying 55 people was stranded on a sandbar in high winds, and all but one had perished by the following day when rescuers from Caernarfon reached the spot.
- 1831 The Rothesay Castle, on a day trip from Liverpool to Beaumaris (August 17.), sank in the sound between Puffin Island and Penmon Point (or Trwyn Du). A lighthouse and a lifeboat station were built here soon after.
- 1832 Cholera outbreak, the first recorded outbreak in Britain 160 are killed in Merthyr and 152 in Swansea. Followed by outbreaks in 1848/9 (which killed 1.682 in Merthyr), 1856 and 1866 which together kill about 5.000 people.
- 1859 The Royal Charter coming from Australia with over 400 passengers, was lost off Anglesey in a major storm (one of the fircest of the century according to some sources). There were only 39 survivors. See here for further details.
- 1865 The only outbreak of Yellow Fever in Britain kills 15.
- 1894 250 men killed at the Albion Colliery, Cilfyndd, near Pontypridd.
- 1913 On 14. October, 439 men were killed in the Lancaster Pit (part of Universal Colliery), Senghennydd, the fourth largest mining disaster in history and Britain's biggest.
- 1918-19 Flu epidemic kills 10.000 people
- 1925 The dam on Llyn Eigiau Dam, Dolgarrog, Gwynedd collapsed killing 16 people.
- 1934September 22. An explosion at Gresford Colliery, near Wrexham, kills 266, almost the entire workforce on shift at the time.
- A Luftwaffe attack on Pembroke Dock produced the longest-lasting fire
since the Great Fire of London. Fire crews required from as far as Cardiff.
It appears that the Germans might have made a serious mistake in bombing this area. There had been a naval dockyard here which was shut in 1926, and it was taken over by the RAF and became their largest seaplane base. It appears thatt the Germans might have thought that they were attacking an active naval dockyard.
- 1941, 19-21 February The town center of Swansea was largely wiped out by fire-bomb raids. 387 people were killed.
- 1941 By the end of the year, 600 houses in Cardiff had been destroyed, and 30.000 damaged. Llandaf Cathedral was damaged.
- 1943 Landing craft sank off Milford Haven with the loss of 78 lives.
- 1960 Flooding in many parts of Wales - including Newtown and the Southern Valleys. Cardiff Arms Parks stands under 1.5 meters of water.
- 1962 Smallpox kills 17 people in South Wales.
- 1966 Aberfan. On 21. October a slag heap slipped onto Pantglas Junior School, killing 116 children and 28 adults.
- 1970 The Brittania Bridge, opened in 1850 over the Menai Straits, was destroyed in a fire.
1996 The Sea Empress oil tanker grounds off Milford Haven and spills its oil onto the Pembroke Coast.