The Orange Order was founded at The Diamond in Co Armagh in 1795 – and this year the county is to host the ‘flagship’ event on Monday.
Eleven districts will join in the demonstration at Bessbrook, with 154 lodges and 5,000 brethren.
Ladies from the Women’s Institution will be joined by several junior lodges.
Seventy bands will accompany the lodges with 60 Lambeg drums.
Meanwhile, in Belfast, as is traditional Belfast County Grand Lodge officers, guests and the Millar Memorial Flute Band leave Clifton Street Orange hall at 9.45am and take up position at Carlisle Circus.
At 10am, the main parade moves along Clifton Street, Donegall Street, and Royal Avenue to the City Hall for a wreath-laying ceremony at the Cenotaph.
Following the act of remembrance, Orangemen and women representing nine districts – accompanied by 60 bands – will proceed via Bedford Street, Dublin Road, Bradbury Place, Lisburn Road, Balmoral Avenue and Malone Road, to the demonstration field at Barnett Demesne.
Among the tens of thousands of onlookers lining the six-mile route will be many global visitors.
Simultaneously, districts will be geared up to celebrate at demonstrations throughout Northern Ireland.
Demonstrations will be taking place in Kesh, Coleraine, Moneymore, Holywood, Saintfield, Laurencetown, Ballymartin, Benburb, Fintona, Fivemiletown, Antrim, Ballymena, Derriaghy, Portglenone, Bushmills, Broughshane and Ballymoney.
The various demonstrations will be covered in a 32-page picture pullout supplement inside Tuesday’s edition of the News Letter.
A 16-page Scarva Day pullout will then follow in Wednesday’s edition.
For full up-to-the minute coverage of the Twelfth throughout Northern Ireland, log on to the News Letter’s website (www.newsletter.co.uk) and visit the specialist segment marked ‘Twelfth 2015’.
And for as-it-happens Twelfth events watch ‘Twelfth 2015 Live’