Although privately held businesses are central to the American economy, little is known about how their assets are distributed among the population. In this study, we describe the household distribution of private business assets in the United States and examine how it has changed over time. Using data from the 1989-2019 Survey of Consumer Finances, we show that the relative number of business owners has remained stagnant at low levels and that assets in privately held firms have become increasingly concentrated among the wealthiest owners over time. At the most recent wave of data collection, the top 1% of households controlled nearly 80% of private business assets, up from about 70% in the late 1980s. We attempt to explain this trend by evaluating how technological change, the financialization of banking, and rising market power have influenced the distribution of private business assets in recent decades. Our findings suggest that all three factors contributed to increasing asset concentration in this sector.