Westmeath is correct. I would go with the spelling Clavin, there are 29 with one being James Clavin of Castletownkindalen, and there is also a Laurence Daly, in Castletownkindalen, Townland Ballynacoska, All in the Union of Mullingar. They would be within 12 miles of the named town in this case Mullingar.
The Poor Law Union boundaries became in most part the
Civil Registration Districts. From the census substitute
Griffith Valuation to which you refer.
Laurence Daly was a tenant of Alice O'Connor Malone and the property was in Chancery (Court) in 1854
property 4A land 4 acres 0 roods 0 perches
4Ba house, outbuillding and land 12.2.30
Griffith Valuation took place 1854. www.askaboutireland.ie
Your Patrick would not be Patrick Daly 1894 Rev. c.c. Catholic Church!
1894 James Clavin, farmer Goreagh Cottage, same in 1881, Kilbeggan 4. mi. from Castletown
The Westmeath telephone book shows 3 Clavin's including one in Mullingar. Addresses are sufficient for mail delivery.
The first page of Daly's has 5 listed in Mullingar.
Westmeath does belong to a not for profit History Foundation (fee based) Castletown-Geoghan RC records date back to 1808.
1901/1911 Census: www.census.nationalarchives.ie
There wasn't much to find you did not already know.