found them - even though they are in two different counties, all the locations are quite close. If you drove the 10km from Rathowen, Co. Westmeath (the nearest major town to Henfield) to Legan church you would pass through, or very close, to both Henfield and Clygeen townlands.
Henfield townland was in the Ballynacarrigy subdistrict, and part of Mullingar registration district. Not only is the area very close to the Longford / Westmeath border, it's also close to the boundaries of three registration districts - Ballymahon, Mullingar & Granard.
The old Co. Longford RC parish which Legan was part of, might have extended into parts of Co. Westmeath.
Shane