Allies and Other Powers
The Federation is a very interesting organization. Founded in 2161 with six signatories. By the late 2200s, humans had settled a thousand worlds spread across a territory almost 4,000 light years across - presumably around the entire Federation; by the late 2300s, it spread irregularly across 8,000 light years, and had 150 members. Some borders remained largely the same for much of this time (e.g., the Gorn-Federation border); some did not. Roughly a quarter of the galaxy has been charted by the end of the TNG era.
The Borg have settled on thousands of planets, and directly control territory thousands of light years across; their effective reach encompasses practically the entire galaxy.
Allies and other powers:
It is for the most part unclear what span of territory is controlled by other powers, with the exception of a wide assortment of single-planet and minor powers.