Dwarf planets
Objects are called dwarf planets if their self-gravity is sufficient to achieve hydrostatic equilibrium and form an ellipsoidal shape.
Largest known Dwarf Planets
Diameter in Km, current distance from the sun in AU (note they have very elliptical orbits, Perihelion = nearest, Aphelion = Farthest)
Pluto 2380km 39.53AU (Aph 49.3 Peri 29.7)
Eris 2326km 96AU (Aph 97.6 Peri 37.8)
2007 OR10 1535km 87AU (Aph 33.0 Peri 100.8)
Haumea 1920x990km 43.31AU (Aph 51.0 Peri 35.0)
Makemake 1430km 45.66AU (Aph 52.8 Peri 38.6)
Eris could be the largest Plutoid
Makemake is smaller than Pluto and "2007 OR10" not quite being spherical - about 1,430km across in one direction and 1,500km across the other.
Dwarf/Minor Planets
Sedna 1800km 486AU (Aph 76.0 Peri 939)
There are currently 8 known smaller Dwarf/Minor Planets between Neptune and Pluto
Note all diameters are approximations
others over 1000km diameter (Dwarf/Minor Planets)
Others
Ixion about 620 km Diameter.
2002MS4 about 960 km Diameter.
Salacia about 921 km Diameter. Moon Actaea (286km)
Varda diameter 716 km Moon Ilmarë (320-360km) confirmed in Sept 2018
Chaos about 612 km Diameter
Hygiea at 444 Km Diameter may be classified as the smallest dwarf planet as it meet all the requirement, it orbits between Mars and Jupiter.
2015 TG387 about 300 km (186 miles) Diameter.
The furthest Dwarf Planet so far discovered (Dec2018) is 2018 VG18, but they’ve nicknamed the planet “Farout.”
Farout is the most distant body ever observed in our Solar System, at 120 astronomical units (AU) away.
It is estimated that there may be 200 dwarf planets in the Kuiper Belt of the outer Solar System and possibly more than 10,000 in the region beyond.
Beyond the Kuiper Belt there is the Oort Cloud.
Finally an interesting video by Isaac Arthur
Colonizing the Oort Cloud