Elavon said more than 1,800 merchant locations nationwide are using its back-office conversion services.
The payments technology unit of U.S. Bancorp announced the milestone last week.
It said its systems handled 4.6 million BOC transactions in August that were valued at more than $400 million.
Elavon, of Atlanta, offers BOC services as part of a suite of automated clearing house conversion services that also includes accounts receivable conversion and point of purchase conversion; the three services enable merchants to convert customers' checks into ACH transactions, at different points in the transaction chain.
BOC takes place at a merchant's back office; Elavon said this makes it a good fit for multilane retailers and large chain stores.
ARC takes place at a lockbox site, and POP occurs at the point of sale.
The company said more than 40,000 merchant sites nationwide are using its Electronic Check Services.