RIC service records have survived. The originals are in the National Archives in Kew, London, with copies in the National Archives in Dublin, PRONI (the public record office) in Belfast and the Garda (police) Museum in Dublin. LDS have also copied them and it is possible to order the films into their libraries. However if you are not able to access any of those options, the police museum in Belfast also has a set of the records and will do a look up for a £25 fee (sterling). See:
https://www.psni.police.uk/inside-psni/our-history/genealogy/
The service records should tell you the person’s county of origin. Note that it was RIC policy not to post a policeman to the county he was born in, nor to a county he had connections in, eg where his wife’s family lived. So expect him to have moved after he married.
In order to join the RIC, you had to be single or a widower without family, & aged 19 – 27 (18, if your father had served in it). You could not marry till you had served 7 years. These rules can be helpful in working out ages and birth years. (Source is Jim Herlihy’s book: “RIC - A short history & genealogical guide” Dublin, 1997).
If you search on findmypast, they have the Irish Petty Sessions records and so you may be able to find court cases your ancestor was involved in by searching on his name plus Irish Petty Sessions.
There is also a specialist website for discussions and enquiries about RIC staff. You might find that helpful: http://irishconstabulary.com
