I mean, he owns a couple hundred thousand acres and it's probably worth a couple billion dollars, which is a lot to mere mortals like me, but the United States is a big country and Bill Gates is a rich person.
Recently, an article in Land Report stated that Bill Gates owns more American farmland than anyone else. He owns 242,000 acres, which is equivalent to the area of Fannin County GA. He owns significantly more farmland than Minnesota's Offutt family and California's Resnick family, which each own 190,000 acres and rank second equal on the list.
Gates owns farmland throughout the country, but his largest holdings are in Louisiana. The Land Report article describes how, after much sleuthing, the author determined that Gates now owns a 26,236-acre Louisiana farm once owned by notorious former Worldcom CEO Bernie Ebbers, who "was convicted of securities fraud, conspiracy, and filing false reports that were instrumental in WorldCom’s $11 billion dollar accounting fraud."
The USDA classifies just over half of the United States 1.94 billion acres as agricultural land. According to the agricultural census, total agricultural land declined from 950m acres in 1997 to 900m acres in 2017. This decline occurred entirely in pasture; harvested cropland increased during this period. Bill Gates owns 0.03% of America's agricultural land.
Different sources provide slightly different numbers for agricultural land use. USDA's Natural Resources Conservation Service produces the National Resources Inventory (NRI) periodically. It shows cropland at 368m acres in 2017 compared to 383m acres in the Agricultural Census. The NRI classifies only 122m acres as pasture compared to 440m acres in the ag census. The census classifies land as pasture that NRI classifies as rangeland. For more on differences in classification of cropland, see this paper by Tyler Lark and co-authors.
Bill Gates is not running farm operations on the land he owns (I assume). He rents the land to farmers. Despite concerns about big money investors buying up farmland, the number of rented farmland acres has not changed appreciably in the past 20 years. About a third of farmland acres are rented from a landlord.
In 2014, the USDA Economic Research Service conducted a comprehensive survey of farmland ownership, tenure, and transfer. It yielded a treasure trove of data, which are well summarized in this report and on this nice data visualization site. I used these data to create the figure below.
Most rented agricultural land is owned by non-operators, i.e., people or companies that do not farm any land. Only about a third of this land was purchased from a non-relative by direct sale or in an auction, as would be the case for investors such as Bill Gates. Half of the rented farmland owned by non-operators was acquired through gifts or inheritance, and about 15% was purchased from relatives. Just under half of this land is owned by individuals, rather than partnerships or corporations.
Investors without a family connection to agriculture do own farmland, and anecdotal evidence suggests they are increasing their holdings. Bill Gates certainly has. However, most absentee-owned farmland appears to be held by the family of farmers or ex-farmers.
I generated the graphs in this article using this R code.