County budget officials said the taxpayer listed that $10 million in sales tax was owed on out-of-state Internet purchases.
The county's chief budget aide, Connie Corso, said the taxpayer had meant to write $1,000.
County budget aides say the $10 million figure should have raised a red flag because the taxpayer would have had to spend $116 million in purchases.
The state Department of Taxation and Finance said it could not immediately comment on how the mistake was overlooked and how it was discovered.
The error reduced first-quarter tax receipts by nearly half.