County Executive Edward Mangano submitted an executive order to the Board of Elections and the county clerk ordering a special election in Nassau's 12th Legislative District on Nov. 6.
The winner of the special election will take office immediately and serve the remainder of Schmitt's term, which ends in January 2014.
County officials said they would not comment on the election process until after Schmitt's funeral on Monday.
Nassau Democrats called Election Day an appropriate date.
"It will save taxpayer money by having it all on one day and will encourage the most political participation," said Mike Florio, spokesman for legislative Democrats.
Republicans and Democrats will hold special nominating conventions to pick candidates for Schmitt's seat. It is unclear who will be nominated but among those who have publicly expressed interest in running is Republican Gary Slavin, a past president of the Massapequa Chamber of Commerce.
Democratic Board of Elections Commissioner William Biamonte said the board has approximately two weeks before printing of general election ballots must take place. "As long as the nominating process moves quickly, we should be fine," he said.
The board expects to mail out the district's 51 military ballots on Monday. Biamonte said he will confer with Republican Commissioner Louis Savinetti, but that the office could send out a second military ballot once nominees in the 12th District are selected.