Hilda Solis, chair of the Los Angeles County Board of Supervisors, announced the decision and said the Biden White House had contacted her about the issue.
"Los Angeles County has a responsibility and an opportunity to care for unaccompanied minors coming to the United States," Solis said. "This is not a border crisis - but, instead, it is everyone's crisis."
The Biden administration has been reaching out to communities throughout the country to find space for housing unaccompanied migrant children who are currently being sheltered in overcrowded Border Patrol facilities.
Long Beach and San Diego have both offered use of their convention centers as temporary shelters.
RELATED: San Diego Convention Center to shelter unaccompanied minors
Details were not immediately available on how many children the Fairplex would house and when the plan would start.
The Pomona Fairplex is run by a nonprofit organization in partnership with Los Angeles County. It hosts the LA County Fair and hundreds of other events in non-pandemic years. It is also currently serving as a COVID-19 vaccination site.