The name is a small clue to how closely this place was tied to its waterlogged surroundings, and the church itself, built on a natural rise of ground in the townland of Roolagh, seems almost designed to keep a watchful distance from those low-lying fields to the west.

The building appears in the ecclesiastical record as early as 1306, when a taxation of the Deanery listed it at a value of 16 shillings and 8 pence per annum. By 1460, a cleric named Donatus O'Hogan held the perpetual vicarage here, and in 1511 a John O'Hogan, clerk of the diocese of Killaloe, presided over a grouped rectory that united Templeachally with four other local churches including Youghalarra and Ballina. The mid-seventeenth-century Civil Survey recorded that the rectory had been made impropriated, meaning that its tithes had passed out of clerical control entirely, conferred upon the Earl of Ormond by patent from the Crown and held, at the time of the survey, by an assignee acting on behalf of the Countess of Ormond. The combined tithes of the united parishes of Templeachally and Kilmastulla were worth £15 in 1640. A single plantation acre of glebe land, the small plot of ground traditionally assigned to support a vicar, lay just east of the churchyard and was already described as waste by that date.

When the antiquarian John O'Donovan visited and measured the ruin in 1840, he found walls of brown quarried sandstone still standing roughly three metres high, and recorded a pointed doorway on the south wall and a twin-light east window whose stone mullion had by then been removed. The fabric visible today includes the east, south, and west walls surviving to something close to full height, while the north wall is largely gone. The west gable shows evidence of a first-floor level, suggesting the building may once have had an upper storey. The east gable retains a partially destroyed traceried window, and the interior of the south wall holds two features that repay close attention: a segmental-arched tomb-niche set into the wall's centre, and near the east end a piscina, a small stone basin used by priests to drain water from the ritual washing of hands and vessels during Mass. This one has a four-centred arch, moulded bases, chamfered jambs, and a drain-hole surrounded by a six-lobed marigold pattern carved into the stone.