Knights Templar are an imperial knight order dedicated to acting as an armed arm of the Imperial Temple, extinguishing heresies deemed dangerous and often serving as one of the first lines of defense against supernatural, religious threats. They can be encountered pretty much everywhere in the Imperium, as long as there is a significant presence of Imperial Religion adherents. They are almost unknown in inrithian or visenian states.
Knights Templar are a centralized organization, that responds to the Pontifex Maximus and Choir of the Divines - in short, to Imperial Temple. There is a Grandmaster of the Knights Templar that resides in its headquarters in the Falon-nir. Beneath him is a council made of several 'ministers' of the Order, that help the Grandmaster govern entirety of it. This includes people responsible for the Order's treasury, training, contacts with the Imperium and other religious organizations, especially like Inrithian Church. There is also another council, gathering from time to time to oversee the Grandmaster's decision. It is composed of overseers of the Knights Templar monasteries throughout the Imperium, called masters of the Order. Each of these places is part training ground, part command centers. Each of the monasteries has certain territory it is supposed to oversee. The division mostly depends on political situation. To avoid causing too much trouble, it is common for a single imperial member state to have a single monastery, but with its size depending on the size of the area it's responsible of. It is also quite often for a monasteris to be internally divided into smaller parts if, for example, a country has more than one significant ethnic group. Each monastery typically takes recruits from the area/ethnic group that it represents. Dislikes between ethnic groups happen quite often.
Serving the Gods... and the Order. It isn't invulnerable to causing problems due to personal ambitions of its Grandmaster, but generally it is an important force of Good in the Imperium, leading a permanent crusade against the forces of Black Pantheon. It mostly steers clear of creatures from Beyond and Pentagram, though - while Knights Templar are expected to stand behind them and innocents, there is an added "if there is no other way" clause in their typical rules of engagement. Combating the Pentagram is left to Raven Knights, Novemberists and Abyssal Knights.
Knights Templar own a lot of villages, manors and castles, enough to (together with money granted by Imperial Temple) supply the Knights Templar with decent equipment. They also receive special boons, as each one of them receives a weapon that is made for the Order by the smiths of High Forge, through some secret rituals.
Demography and Population
Becoming a candidate to the Knights Templar order isn't hard, all that is required is being of sensible age, being physically fit and being an ardent worshipper of the Imperial Religion - exact Gods you prefer doesn't matter, as long as they aren't considered evil. White Pantheon and few Black Pantheon Gods but with more positive spin (like Shadow as a God of self-improvement and not of revolution and anarchy). Vassal religions adherents are accepted, as long as they hail from the religions that actually accept their vassal status. So, Twice-Seven worshippers can be met among the Knights Templar (even if its rare), while Inrithians simply doesn't happen. The training, however, is ardurous, and most of the candidates fall before finishing it and becoming a full knight-brothers/sisters. It is estimated that 80% neophytes is purposefully forced to resign, due to Knights Templar wishing to have only the best in their ranks. Species and gender matters little, though knight-sisters are much rarer. The ratio varies between 9 to 1 and 7 to 3, depending on how the local society treats women. The closer to equality, the more knight-sisters. The only difference are lands of Varcubi, where ratio is exactly reversed.