The proportion of rental units owned by individuals used to be a large majority, but has been falling and recently dipped under 50%. As of the 2018 Rental Housing Finance Survey [1], there were 48 million rental units in the United States, with ownership breaking down as:
41% individual
37% LLP, LP, or LLC
3% real estate corporation
3% nonprofit organization
2% general partnership
2% trustee for estate
2% real estate investment trust (REIT)
10% other or unreported
The number DIY managed by the owner or owner's family/associates is similarly down, to 42%, with 54% of units now professionally managed (4% other/unknown).I don't have numbers, but I'd imagine it looks even more skewed in the direction of professional landlords if you looked at major cities.