LLANALLGO (LLAN-ALLGOV), a parish in the hundred of TWRCELYN, county of ANGLESEY, NORTH WALES, 7 miles (E. by N.) from Llanerchymedd, containing 417 inhabitants. This parish, which is of considerable antiquity, derives its name from the dedication of its church to St. Alltgo, son of Caw o Vrydain, by whom it was originally founded, about the commencement of the seventh century. It is situated on the coast of the Irish sea, by which it is bounded on the east, and, though of small extent, is rich in mineral treasures, and contains a large proportion of fertile land, which is for the most part enclosed and in a good state of cultivation. The great range of limestone strata, which stretches from Flintshire through the county of Denbigh, by Great Orme's Head, and is continued under the bay of Beaumaris and along the northern shore of Anglesey, terminates at Moelvre, in this parish, where are extensive quarries of clouded, or variegated, marble, in considerable estimation for the variety and brilliancy of its colours, and the high polish of which it is susceptible. Great quantities of this marble, which is well adapted for mantelpieces and ornamental statuary, are obtained from these mines, and shipped off to various parts of Great Britain. In this parish are also some quarries of black and grey marble, of good quality, which afforded materials for the construction of the pier and the erection of the lighthouse at Holyhead.
The living is a perpetual curacy, annexed to the rectory of Llaneugrad, in the archdeaconry of Anglesey, and diocese of Bangor, and in the patronage of the Bishop of Bangor. The church, dedicated to St. Gallgov, is a small but handsome cruciform structure, containing in the east window of the chancel, which is of elegant design, some fragments of ancient stained glass : it was thoroughly repaired in 1831. Near it is Fynnon Gallgov, or "St. Gallgov's Well :" its waters, which are strongly impregnated with sulphate of lime, were formerly held in high veneration for the miraculous cures ascribed to them, and are still regarded as highly beneficial in some chronic diseases. Adjoining the west front of the church is Capel Fynnon, or "the chapel of the Well," a small neat edifice, formerly appropriated to the use of the votaries of the patron of the spring, to whose influence the miraculous efficacy of its waters was attributed. In the adjoining parish of Llaneugrad are the ruins of an ancient chapel, formerly belonging to the church of this parish, and still called Capel Lligwy, from the name of the farm on which it is situated. There are places of worship for Independents and Calvinistic Methodists. The average annual expenditure for the maintenance of the poor amounts to £91. 17.