It's part of her 2012 budget that will be unveiled Tuesday.
Preckwinkle says most of the layoffs will occur in her administration and within Cook County's health system.
Preckwinkle announced a sales tax rollback of a quarter cent of the 1-percentage-point sales tax increase the county board passed in 2008.
Cook County is facing a projected $315 million budget shortfall.
Preckwinkle says the projected layoffs are in part due to the county's unions rejecting an offer of eight unpaid days off next year to save 500 jobs.
The Associated Press contributed to this report