A Docket Number is the identifier FMCSA assigns when it grants a company operating authority, distinguished by a prefix — MC for most carriers and brokers, FF for freight forwarders, or MX for Mexico-domiciled carriers. "MC number" and "docket number" are used interchangeably in the industry, since MC is by far the most common prefix. A single company can accumulate multiple docket numbers over its history, for example if it originally registered under one authority type and later added another, and each docket has its own status (Active or Inactive) independent of the others. The system traces back to the Interstate Commerce Commission (ICC), which is why the numbering convention persists even though the ICC itself was dissolved in 1995 and its functions transferred to FMCSA and other agencies. When people say "check their docket," they typically mean verifying that the associated operating authority is active and in good standing, not just confirming that the number exists on file somewhere.
A broker's docket number and their USDOT number are usually different values — the docket specifically reflects their broker operating authority.
Listed in the Docket / MC Numbers section, and shown as the 'MC' ID chip, on every carrier and broker profile.