Washington state election officials said that there are 450 drop boxes statewide, and there are discussions about adding more.
Typical security measures for drop boxes include video surveillance, locks, tamper-resistant seals and chain-of-custody logs that are completed each time ballots are collected.
In Pennsylvania, a federal lawsuit by the Trump campaign and Republican National Committee has cast drop boxes into a legal gray area.
Democratic state lawmakers are countersuing to get a judge to clarify that drop boxes are legal.
Suburban Delaware County is plowing ahead with its plans for drop boxes without waiting for the outcome of the legal dispute, said County Council member Christine Reuther, a Democrat.