Ciarán Redican's site has a nice description of the French forces' arrival and march through Leitrim. The French had come to help the rebels in August 1798, but it all ended in surrender to the English forces at Ballinamuck the following month. The following is an exerpt:
The French arrived at Cloone tired, worn, and hungry. The chains of their remaining cannons were stolen here rendering them useless. Whilst in Cloone, they were treated well by a loyalist whose house they comandeered. General Humbert and his officers dined at the house with the local parish priest and curate. Six bullocks were grilled on the gates of the Prodestant Church for the troops. The villagers at Cloone persuaded Humbert to wait for a day as they promised him 10,000 reinforcements. This turned out to be a mistake as it allowed the Crown Forces to be reinforced.
After the French left Cloone, hundreds of Pikemen arrived, but were dissuaded from following the French by the local Parish Priest who explained to them that it was a lost cause. The Crown Forces had caught up with Humbert. The battle was waged at Ballinamuck, it was a very short affair. The French were given an honourable surrender and were treated as prisoners of war. The Irish were given no such honour, they were hunted down and hung. General Blake, the Irish Commander was caught in a bog and was hanged from the shafts of a cart. The area around Ballinamuck was laid waste by the Crown forces, pillage, plunder, and mayhem were the order of the day.