Yes, all Maryland public library systems (Directory of Public Libraries at http://directory.sailor.lib.md.us/pub_use/county_map.cfm ) accept materials borrowed from any Maryland public library systems for return, subject to that library's current fines/fees, policies and procedures.
However, it is recommended that any item borrowed through the Marina or OCLC Interlibrary Loan Services should be returned to a BCPL branch. In order to clear your account, please return items with any carry bags or paperwork, book bands, barcodes found in or on an interlibrary loan item.
Please ask for a receipt showing the date, what materials you returned, and what fees/fines were paid, if any.
Since the item must be sent from the other library system back to Baltimore County Public Library before it can actually be checked in, your library account (http://catalog.bcpl.lib.md.us/polaris/logon.aspx) may reflect that delivery delay under the Items Out and/or Fees (if overdue) area.