O'Connor Desmarais & Co. is an accounting firm in McLean. O'Connor Desmarais & Co. specializes in bookkeeping, financial advising and accounting services for small- to mid-sized businesses. However, during tax season, it also provides tax preparation services from the same offices. The founders, Carl F. Desmaris, C.P.A. and Terry O'Connor, C.P.A., have decades of combined experience.