Dear Lady Di,
I have asked the same questions and the answers are to be found in vol 3 of English Army Lists 1661 to 1714 by Charles Dalton and tells us that Tho. Crouch was a Captain in Viscount Lisburne's Regiment of Foot, which was raised principally in Co. Huntington and served throughout the Irish Campaign (only being disbanded in England in 1697). As for Tho. himself, his was not on any list after October 1689. During the course of a review of Infantry Regiments at Dundalk Camp between the 18 and 28 October 1689 he was listed with the letter 'S' next to his name - signifying that he was sick. My understanding is that the site of the camp in Dundalk was poorly chosen and that as a consequence many of the soldiers there fell ill and died. Tho. however appears to have survived and returned back to Hertfordshire, where he married Anne, daughter of Bernard Turner of Buntingford. I'm not exactly sure when they married, but Tho. was buried on 28 Mar 1701 (so possibly his health had been weakened by his experiences in Ireland). In any event Tho. was on the side of King William.
I hope that this is helpful.
Many regards,
Alfred21
NB As regards Viscount Lisburne himself, I think that he will have been Adam Loftus, who was killed by a cannonball at the Siege of Limerick on 15 September 1691.