That tower is not merely a bell-tower or a decorative remnant; it was built for defence, equipped with a murder-hole guarding the entrance from the church, a spy-hole in the first-floor wall overlooking the nave and commanding the murder-hole below, and a mural staircase winding through the thickness of the walls between floors. Somewhere within the upper masonry, obscured for a long time by ivy, a bellcote with two openings was noted by John O'Donovan around 1840, and a conservation project completed in 2019 may have brought it back into view. That same project, funded by Wexford County Council, also uncovered an earlier twelfth-century window whose dressed green stone had been reused in the first-floor south wall, its outer rebate still cut for a shutter.

The church takes its dedication from St. Moininne, one of the more widely travelled figures in early Irish hagiography. Her legend connects her variously to the Uí Eachach Comha of Co. Down and to the Cenél Eoghainn of Tyrone; she was reputedly baptised by St. Patrick and founded a nunnery at Faughart in Co. Louth, a site also associated with the birthplace of St. Brigid. She is said to have visited St. Iobhar at Beggerin in Co. Wexford, linking her to this corner of Leinster, and later founded a convent at Killevy on Slieve Gullion in Co. Armagh, which eventually became a house of Augustinian nuns and lasted until the Dissolution. By 1615, when Thomas Ram, the Protestant bishop of Ferns, carried out a visitation of his diocese, the church at Kilmannan had a rector named Jacob Prendergast and both church and chancel were recorded as being in repair.

The wider site rewards a slow look. A bullaun stone, a basin-shaped hollow worn or carved into a boulder and commonly associated with early ecclesiastical sites, lies roughly 50 metres to the south-west in Woodstown townland. About 320 metres to the south-south-east is the site of St. Mannan's Well, where patterns, the traditional gatherings of prayer and communal observance held at holy wells, were celebrated on the 6th of July.