[16] Three USL Championship teams, Penn FC, the Rochester Rhinos and the Richmond Kickers, also announced plans to move to League One by 2020 due to financial difficulties.

[17][18][19] On October 2, 2018, the tenth and final founding member was revealed to be the reserve team of FC Dallas.

[23] The first League One game was played on March 29, 2019, when Tormenta FC defeated Greenville Triumph SC 1–0 before a crowd of 3,519 at Eagle Field in Erk Russell Park.

[31] Rochester had announced in 2018 their intentions to join League One for the 2020 season, though stadium delays and other financial issues kept the club on hiatus for four years.

[32][33] On October 5, 2021, the USL announced it had awarded Lexington Pro Soccer an expansion team for the 2023 season.

[36][37][38] On June 3, 2022, USL announced that they had granted a group based out of Wilmington, North Carolina the exclusive rights to pursue a League One expansion team for the area with the goal of joining in 2024.

[42] Following the conclusion of the 2022 regular season, FC Tucson announced a self-relegation back to USL League Two.

[55] In October 2024, the league granted expansion teams to Corpus Christi, Texas, and Boise, Idaho.

On November 14, 2024, the USL announced that it had terminated Northern Colorado Hailstorm FC's franchise agreement and that Central Valley Fuego and the league "had come to a mutual decision to part ways.

"[58] On February 14, 2025, the league granted an expansion team to Paterson, New Jersey to begin play for the 2026 season at historic Hinchliffe Stadium.