All states have laws governing so-called unclaimed property. Financial institutions, including brokerage firms, banks, and transfer agencies, are required to report personal property that has been unclaimed and then remit that property to the state.
Your mutual fund account (including the fund shares and any uncashed distribution checks in the account) may be considered unclaimed if certain criteria (which vary by state) are met, such as any of or a combination of, mail being returned as undeliverable, uncashed checks or, in some circumstances, a lack of account activity for an extended period of time.
Once property meets the unclaimed property requirements in your state of residence, it must be turned over to the state in a process known as "escheatment."