It’s small landlords that own the vast majority of SFH rentals. Most of the rental supply is owned by them.

Wolf Richter does some great articles on that, based on data from John Burns Research and Consulting. Their data suggests the rates of corporate ownership are very small. There is a myth though that Wall Street is out buying massive percentages of homes, but the data doesn’t seem to support that. They appear to own very little of the total market. Here’s the info from wolfstreet:

80% (11.2 million houses) are owned by mom-and-pop landlords with 1-9 rentals

14% (1.96 million houses) are owned by landlords with 10-99 units

3% are owned by landlords with 100-999 units

3% (around 400,000 houses) are owned by a handful of huge landlords with 1,000+ units each.

The data for the above comes from John Burns Research & Consulting, based on its aggregation of public records data and Census Bureau data.