[5] The Finn River rises on the slopes of Knoppane, a hill just to the south of Slieve Beagh in the south-east of County Fermanagh.

[3] It meanders around both Rough Hill and Gola, two neighbouring townlands in the north-west of County Monaghan that are a short distance north-east of Roslea.

At a place between New Bridge and Aghafin House,[15][16] the river meanders around a sharp bend, flowing in a south-easterly direction for almost two miles, entirely within County Monaghan, between the townland of Aghafin,[17] just north-east of Clones, and the townland of Nook,[18] just south-east of Stonebridge.

[3][4] The Finn flows on through Wattlebridge, a hamlet in the south-east of County Fermanagh,[3][27] then enters Upper Lough Erne nearby.

[2] The river flows into a narrow channel of the lough at this place, where the townland of Edergool (Irish: Eadarghabhail, meaning 'Between Forking Streams' or 'Between (Stream) Forks'[30][31][32]) in County Fermanagh meets the townland of Castlesaunderson Demesne, where Castle Saunderson is located, in County Cavan.

[3] The south-western part of the Finn River cuts Drummully off from the rest of County Monaghan.

[46] The district and the various types of parish (both civil and ecclesiastical) are named after the Drummully Monastic Site.

[44] This monastic site and ruined former parish church are on a hilltop in the townland of Drummully, just inside County Fermanagh, very near Wattlebridge.

These include: Derrygannon Bridge, right beside Derrygannon Community Hall,[8][9] located about 3 miles north-west of Roslea, which carries the Eshnadarragh Road across the Finn;[47] and Derryvollan (also spelled as Derryvullan) Bridge, located a few miles north-north-east of Roslea, which carries the Deerpark Road across the Finn from County Fermanagh into County Monaghan.

[49] Lisnawesnagh Bridge, which is constructed of stone, is located just north-east of Roslea and also carries the Deerpark Road across the Finn.

This bridge is on the south-western edge of Spring Grove Forest and carries the Clogh Road across the Finn.

[3] A small sideroad known locally as 'the Gorry Lane' is beside New Bridge, part of the 'lane' being on the edge of Spring Grove Forest.

[4] The Finn flows under Stone Bridge, built in the early nineteenth century and located in the hamlet of Stonebridge, between Clones and Smithborough in West Monaghan.

[4] Conaghy Castle, formerly a Mac Mathghamhna (MacMahon) fortification, was probably quite close to the river at this point, the 'castle' almost certainly having been on a small hill overlooking the site of the later aqueduct.

[55] The Finn flows under the now derelict Annaghkilly Railway Bridge, located close to the former Ballynure Demesne, immediately south of Analore.

There are two bridges at Derrykerrib, both of which are modern, concrete structures, located slightly to the north of the Finn River's mouth.

The new bridge spans this channel, which was cut on the Derrykerrib shore of Upper Lough Erne.

This new channel allows boats to sail, via the Finn River, as far as the jetty at Castle Saunderson in County Cavan.

The bridge is just over a mile south-west of Knockatallon, a hamlet in the north-west of County Monaghan, and carries a sideroad called the Corragunt Road across a small stream.

[70][71][72][73] Ballynure Viaduct is located immediately south of Analore, a hamlet in West Monaghan.

[74] The viaduct formerly carried the Dundalk and Enniskillen Railway across a small ornamental lake beside the main entrance into the demesne.

[56][75] The viaduct formerly carried the Dundalk and Enniskillen Railway across the southern part of the townland of Annaghkilly, just south-west of Analore.

Nancy's Bridge was built in the late 1850s or early 1860s and carried a sideroad over the Cavan Town to Clones railway line, very near the Finn River.

[80][81][82][83] On a small hilltop overlooking the south-western end of the Finn River, very near Wattlebridge, is Drummully Monastic Site.

[3][84] The site, which is in the townland of Drummully and is just inside County Fermanagh, is right beside Clogher Market, being very close to Gortnacarrow Bridge.

The church here was probably dedicated to Saint Mochomma originally, and was later under the authority of the Ó Gabhann (O'Gowan or Goan) dynasty, who held the hereditary position of airchinnech (erenagh) of this area in later Gaelic times.

[84][85] An Early Christian site, Drummully later developed into a small monastery and parish church in the Medieval Era.

St. Alphonsus's Church is in an area known as the Connons, and was built in the early 1840s,[86][87] just before the outbreak of the Great Famine.