Tullygallan (Irish derived place name, Tulaigh Dhalláin, meaning 'The Hill of Dallán Forgaill') is a townland in the civil parish of Drumhome, Roman Catholic parish of Drumholm, barony of Tirhugh, County Donegal, Ireland.
Tullygallan is bounded on the north by Tullymorin townland, on the west by Rossmore, Rossyvolan, Tullyearl and Tullywee townlands and on the east by Raneany West and Tullyleague townlands. Its chief geographical features are the Laghy River, Tullygallan Hill, which reaches a height of 169 feet, woods, small streams and a spring well. Tullygallan is traversed by the national primary N15 road (Ireland), minor public roads and rural lanes. The townland covers 175 acres.
The original name of the townland was Tulaigh Dhalláin meaning 'The Hill of Dallán Forgaill'. Dallán was a friend of Saint Conall Cael of Inishkeel, further up the coast of Donegal, where he later died, so he may have rested in the townland on his way to visit Saint Conall. The earliest surviving mention of the name is from 1608 in "A booke of the Kings lands founde upon the last generall survey within the province of Ulster" found in the MS. Rawlinson A.237 (Analecta Hibernica, Vol. 3, 1931, page 163) where it states that the barony of Tyrhugh was divided into different precincts, one of which was called 'Tullygallane' which comprised one-quarter of a ballybetagh. There is a similar named townland in the mountain to the east of Tullygallan called 'Tullygallan, Tullywee, Oughtnadrin Barr', which probably formed part of the townland in 1608. Other early mentions are under St. Dallan's feast day of 29 January in the 'Martyrology of Donegal' published 1630 by Mícheál Ó Cléirigh (which states- Ata Tulaigh Dallain for it Tir Conaill, meaning 'There is also a Tulach Dalláin still in Tir-Conaill') and in John Colgan's 'Life of Saint Dallán' contained in his 1645 work entitled Acta Sanctorum Hiberniae, page 204, wherein he refers to different locations associated with Dallán, including 'Tulach Dalain and Tulach Dalani' in Raphoe diocese.