Tassan (Irish: An tEasán) is a townland in the parish of Clontibret in County Monaghan, Ireland.

The townland of Tassan or Tasson is situated approximately two miles north east of Annyalla, close to the border with Northern Ireland, between the towns of Monaghan and Castleblayney, off the old N2 primary road, which linked Dublin and Derry.

The battle was the earliest clash between the two sides, with the Irish led by Hugh O'Neill and the English by Sir Henry Bagenal.

The captains' mine offices remain standing, and the site is largely grassed over with spoil heaps visible near Tassan Lough Natural Heritage Area.

In 1939, the team won the Dr. Ward Cup Final re-play against Killanny, which was held in Castleblayney on Sunday 21 April 1940.