No year in Irish history is better known than 1690. No Irish battle is more famous than William III's victory over James II at the River Boyne, a few miles west of Drogheda. James, a Roman Catholic, had lost the throne of England in the bloodless "Glorious Revolution" of 1688. William was Prince of Orange, a Dutch-speaking Protestant married to James's daughter Mary, and became king at the request of parliament. James sought refuge with his old ally, Louis XIV of France, who saw an opportunity to strike at William through Ireland. He provided French officers and arms for James, who landed at Kinsale in March 1689. The lord deputy, the Earl of Tyrconnell, was a Catholic loyal to James, and his Irish army controlled most of the island. James quickly summoned a parliament, largely Catholic, which proceeded to repeal the legislation under which Protestant settlers had acquired land.

http://www.irelandseye.com/aarticles/history/events/dates/ch5.shtm 

Sir Cloudsley Shovell's squadron of warships escorted William's fleet of about 300 vessels across the Irish Sea into Belfast Lough on 14 June 1690. The best moorings had been taken by Schomberg's fleet, so it was not until noon that William's navy and supply ships dropped anchor. The king stepped ashore at Carrickfergus, sat briefly on a chair brought to him, mounted his horse and made his way to Belfast. Never before had Belfast greeted so many men of distinction.

On 19th June 1690, King William set out from Belfast to Lisburn and from there towards Newry. James II pulled back from Dundalk to Drogheda and, just upstream from the port, his army took up battle positions along the south bank of the River Boyne.

The battle began on Tuesday 1st July, with an artillery barrage and William decided on a frontal assault across the river at Oldbridge, while he sent his right wing upstream in a feint which successfully drew most of the French away. The Dutch Blue Guards had to wade up to their armpits at Oldbridge, fiercely opposed by Tyrconnell's cavalry, but in the end the Williamites triumphed by superior firepower and weight of numbers. Both the Duke of Schomberg and Rev George Walker were killed in the fighting.  http://www.bbc.co.uk/history/timelines/ni/battle_boyne.shtml 

Account of the battle  http://www.bcpl.net/~cbladey/battle.html 

Official site http://62.73.162.179/ Excellent images

Heritage of Ireland

http://www.heritageireland.ie/