The army of Gondor at the end of the War of the Ring and the beginning of the Fourth Age is a depleted and exhausted one, even though they are the victors!
The majority of Gondor's forces are citizen soldiers, only pressed into service in times of desperate need, such as the War of the Ring! So at the end of the war, much of the manpower of Gondor is going to be diverted into more peaceful pursuits: farmers, fishermen, craftsmen and merchant folk. These militia men can be called upon, but only at a great cost to the economic rebuilding of Gondor.
There is a standing army, a core of professional soldiers, principally based in Minas Tirith in the north and at Dol Amroth in the South. These warriors will form the basis of King Aragorn's plans to clear Gondor of stragglers, protect his borders, push into Ithilien and perhaps, eventually, re-establish the lost Kingdom of Arnor.
I have described the troops qualitatively, but not with any rule set in mind. More just as an indication that I can consider during the campaign. The descriptions I have used are, in descending order: elite, veteran, regular, average, poor (untrained or unmotivated or both).
The army of Gondor, clockwise by province, is as follows:
Arnorien
Standing Forces
One Company (200 men) of household foot troops in the service of the Lord of Anorien. Average Quality.
One Garrison Company (200 men) of militia protecting the beacons strung along the White Mountains towards Rohan. Poor Quality.
Available Levy
One Regiment of foot archers (600 men). Average quality.
Ithilien
No forces
Minas Tirith
Standing Forces
1 Guards regiment under the command of Hurin, Warden of the Keys
1 company of Guards of the Fountain Court (200 men) - Elite quality
2 companies of Citadel Guards (400 men) - Veteran quality
3 regiments Minas Tirith Warriors (1800 men) - Heavy infantry armed with spear and sword - Regular quality.
1 regiment of Minas Tirith Archers (600 men) - armoured archers - regular quality.
2 regiments of Minas Tirith cavalry (300 riders) - heavy cavalry with spears - veteran quality
Prince Faramir's White Company - 1 company of the Prince of Ithilien's personal guard (200 men) - Elite quality
1 regiment of Ithilien Rangers (600 men) - foot archers, skirmishers and ambushers - veteran quality
1 regiment of Gondorian Rangers (600 men) - foot archers, skirmishers - regular quality
Levy Forces
3 regiments of Minas Tirith militia (1800 men) - spear foot - poor quality
Lossarnach
Lossarnach is a relatively densely populated region immediately south of Minas Tirith. The region is fertile farming and grazing land, and also lies along the main trade route between Minas Tirith and Pelargir. It is the region that has perhaps been the least touched by the War of the Ring, and so remains a prosperous and well-settled region.
Standing Forces
1 squadron of household heavy cavalry (50 riders) in the service of Lord Forlong the Fat - veteran quality
3 regiments of Lossarnach heavy foot (1800 men) armed with axes and shields - regular quality
1 regiment of Lossarnach scout cavalry (150 riders) - lightly armoured spear cavalry - veteran quality
Levy forces
3 regiments of spear foot (1800 men) - poor quality
1 regiment of unarmoured foot archers (600 men) - average quality
Lebennin
Lebennin is the most densely populated province of Gondor after the great city of Minas Tirith itself. Lebennin's principal city is Pelargir, the trading port of Gondor. It is home to the Gondorian Navy and a relatively prosperous trading middle class who can afford arms and horses. Consequently, Lebennin has a mix of forces, mainly focussed on protecting the province from raids by corsairs from Umbar and the men of Harad.
Standing forces
2 squadrons of heavy horse (100 riders) in the service of the Lord of Lebennin.
Gondorian Navy - 10 ships survived the attack of the corsairs in the War of the Ring. Each ship can carry 50 Gondorian marines.
1 regiment of Gondorian Marines (600 men) - medium armour mixed foot and archers - veteran quality
2 regiments of Pelargir Guardsmen (1200 men) - heavy spear foot - regular quality
1 regiment of Pelargir Archers (600 men) - armoured archers - regular quality
2 regiments of Pelargir medium cavalry (300 riders) (maintained by the burghers of Pelargir) - regular quality
Levy forces
1 regiment of Ethel Anduin fishing folk (600 men) - handy in a boat or ashore - skirmishers
1 regiment of Lebennin foot archers (600 men) - shortbow - poor quality
2 regiments of rural Lebennin militia (1200 men) - spear and shield
Principality of Dol Amroth (Belfalas province)
Belfalas province has long been held by the Princes of Dol Amroth, who claim Numenorean and Elvish descent. The current Prince, Imrahil, owes allegiance to the King of Gondor, but in reality he conducts his affairs semi-autonomously from the remote capital of Minas Tirth. The fortress of Dol Amroth is home to the Prince and his small but high quality standing army, which is needed to protect the long coastline of Southern Gondor from the predations of the Corsairs from Umbar.
Standing army
1 squadron of the Prince of Dol Amroth's household Cavalry (50 riders) - elite super heavy cavalry
1 regiment of Swan Knights (150 riders) - heavy cavalry - veteran quality
2 regiments of heavy spear foot (1200 men) - veteran quality
1 regiment of foot archers (600 men) - regular quality
1 regiment of Belfalas Rangers (600 men) - archers and skirmishers - regular quality
Levy forces
2 regiments of Belfalas Militia (1200 men) - spear and shield - poor quality
1 regiment of Belfalas skirmishers (600 men) - slings, javelins, shortbows - poor quality.
Anfalas
Remote, sparsely populated and rural, Anfalas has no major cities or fortifications and the only standing force is the household of the Lord of Anfalas, Golasgil. However, Anfalas is also where the rangers from the Pinnath Gelin patrol to protect what little they have. Whilst the rangers are levy strictly speaking, their reaction to external threat is very quick and so can be considered as a standing force for the purpose of the campaign.
Standing forces
Lord Golasgil's household: 1 troop of heavy cavalry (12 riders) - veteran quality
1 company of heavy infantry (200 men) - regular quality
Hirluin the Fair, Captain of 1 regiment of Pinnath Gelin Rangers (600 men) - archers, skirmishers, ambushers
Levy forces
1 regiment of Anfalas rural militia - scantily equipped
hunters
and herdsmen and men of little villages- poor quality
Blackroot Vale
Located near the paths of the dead, the hardy men of Blackroot Vale are relatively secure from both Corsairs and Orcs, and so can readily provide a levy when called upon, which is often.
Lord Duinhir
with his sons, Duilin
and Derufin.
1 company of household heavy infantry (200 men) - sword and shield - veteran quality
1 regiment of Blackroot Vale Rangers (600 men) - ambushers, archers, skirmishers - veteran quality
Ringlo Vale
The upper reaches of the Ringlo River breeds also breeds hardy folk that are much prized in times of war.
Like the men of Blackroot Vale, the men of Ringlo Vale are quick to respond with their levy when called upon.
Lord Dervorin's household: 1 company of heavy foot (200 men) - veteran quality
1 regiment of Ringlo Vale foot (600 men) - regular quality.
Lamedon
The sparsely populated high country of Lamedon also breeds hardy souls noted for their ferocity on the charge and their war-cry that scatters lesser men and orcs.
The men of Lamedon have few permanent settlements and no recognised lord. They elect a war chief, who is usually the boldest and bravest, to represent them when needed. But like the men of Ringlo and Blackroot Vales, the men of Lamedon are quick to volunteer and their service is highly valued by the Kings of Gondor.
1 regiment of unarmoured highland foot (600 men) - veteran quality, ferocious charge.
Tolfalas
Tolfalas is the island off the coast of the Ethir Anduin. A mountainous and inhospitable place, Gondor maintains a small garrison of marines to keep watch on the movements of corsairs and to light the warning beacon at the top of the island.
1 company of Gondorian Marines (200 men).
2 Gondorian navy vessels.
Conclusion
So Gondor is described. Now to consider the scattered remnants of the Haradrim and Mordor armies.
To summarise, Gondor's forces, both standing and levy, are approximately 38 regiments of foot (about 23,000 men) and 7 regiments of horse (about 1200 riders). That may seem a lot, but Gondor has a lot of work to do and is still surrounded by threats on all sides.