Legal Question in Landlord & Tenant Law in Illinois

Not enough info. Was this a written or oral lease? Month-to-month or longer? Security deposit funds could be applied to anything but it sounds like your organization may owe more rent than the security deposit might cover and there could be damages to the place you rented. If it was a lease for a longer period of time, say a year, they could hold you liable for what they lose on the rent over the rest of your lease term after you stopped paying. Simply moving doesn't stop your liabilities from running. The only "good" news is that Illinois does require the landlord to try to "mitigate" its damages -- that is try to minimize them, by trying to relet the place, but you may be liable for the differnce if the landlord rents for less. Time to get a lawyer. If you're a true non-profit (501c3?) you might be able to get pro bono legal services (ie. for free). Good luck.