SECURITIES AND EXCHANGE COMMISSION

                             Washington, D.C. 20549



                                    FORM 8-K

                                 Current Report
                        Pursuant to Section 13 or 15(d)
                     of the Securities Exchange Act of 1934


        Date of Report (Date of earliest event reported): December 12, 1999

                            21st Century Telecom Group, Inc.
    ----------------------------------------------------------------------
             (Exact name of Registrant as specified in its charter)


                                    Illinois
    ----------------------------------------------------------------------
         (State or other jurisdiction of incorporation or organization)




                333-47235                             36-4076758
    -----------------------------         --------------------------------
        (Commission File Number)       (I.R.S. Employer Identification Number)

                               World Trade Center
                          350 North Orleans, Suite 600
                             Chicago, Illinois 60654
    ----------------------------------------------------------------------
               (Address of principal executive offices) (Zip Code)


                                 (312) 955-2100
    ----------------------------------------------------------------------
              (Registrant's telephone number, including area code)

<PAGE>


Item 5.   Other Events.

          On December 12, 1999, 21st Century Telecom Group, Inc. (the "Company")
     entered  into an  Agreement  and Plan of Merger (the  "Merger  Agreement"),
     among RCN  Corporation  ("Parent"),  21st  Holding  Corp.,  a wholly  owned
     subsidiary of Parent  ("Sub"),  and providing  for the  acquisition  of the
     Company by Parent in a transaction structured as a merger (the "Merger") of
     Sub with and into the Company,  with the Company  surviving  the Merger and
     becoming a wholly owned subsidiary of Parent.

          Consummation of the Merger is subject to certain conditions, including
     the  expiration or earlier  termination  of any  applicable  waiting period
     under the Hart-Scott-Rodino  Antitrust Improvements Act of 1976 and receipt
     of required regulatory approvals.  In addition,  consummation of the Merger
     is subject to the receipt of tenders and consents  from holders of at least
     a majority of the Company's 12-1/4 Senior Discount Notes Due 2008 ("Notes")
     and the debt securities  underlying the Company's 13-3/4% Senior Cumulative
     Exchangeable Preferred Stock, $0.01 par value ("Exchangeable Preferred") to
     remove  certain  restrictive  covenants  applicable  thereto at a price not
     exceeding 101% of their accreted value, in the case of the Notes,  and 101%
     of  their  liquidation  preference,  in the  case  of the  debt  securities
     underlying the  Exchangeable  Preferred.  A copy of the Merger Agreement is
     filed herewith as Exhibit 2.1 and  incorporated  by reference  herein.  The
     description of certain terms of the Merger  Agreement set forth herein does
     not  purport  to be  complete  and  is  qualified  in its  entirety  by the
     provisions of the Merger Agreement.

          A copy of the Merger  Agreement  is filed  herewith as Exhibit 2.1 and
     incorporated by reference  herein.  The description of certain terms of the
     Merger  Agreement  set forth  herein does not purport to be complete and is
     qualified in its entirety by the provisions of the Merger Agreement.

Item 7.   Financial Statements and Exhibits.

     (c)  Exhibits.

         Exhibit No.

          2.1  Agreement and Plan of Merger, dated as of December 12, 1999,
               among RCN Corporation, 21st Holding Corp. and 21st Century
               Telecom Group, Inc.

<PAGE>


                                   SIGNATURES


     Pursuant to the  requirements  of the Securities  Exchange Act of 1934, the
Registrant  has duly  caused  this  report  to be  signed  on its  behalf by the
undersigned hereunto duly authorized.

                                               21st CENTURY TELECOM GROUP, INC.



         Dated: December 14, 1999                By: /s/  James K. Nugent
                                                     --------------------
                                                     James K. Nugent
                                                     Corporate Controller

<PAGE>
                         21st CENTURY TELECOM GROUP, INC

                                    FORM 8-K

                                  EXHIBIT INDEX


         Exhibit No.

          2.1  Agreement and Plan of Merger, dated as of December 12, 1999,
               among RCN Corporation, 21st Holding Corp. and 21st Century
               Telecom Group, Inc.
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{"company-data": {"conformed-name": "21ST CENTURY TELECOM GROUP INC", "cik": "0001056751", "assigned-sic": "4899", "irs-number": "364076758", "state-of-incorporation": "IL", "fiscal-year-end": "0331"}, "filing-values": {"form-type": "8-K", "act": "34", "file-number": "333-47235", "film-number": "99774487"}, "business-address": {"street1": "WORLD TRADE CENTER CHICAGO", "street2": "350 N ORLEANS, STE 600", "city": "CHICAGO", "state": "IL", "zip": "60654", "phone": "3124702100"}, "mail-address": {"street1": "WORLD TRADE CENTER CHICAGO", "street2": "350 N ORLEANS STE 600", "city": "CHICAGO", "state": "IL", "zip": "60054"}}
SECURITIES AND EXCHANGE COMMISSION

                             Washington, D.C. 20549

                                    FORM 8-K

                                 Current Report
                        Pursuant to Section 13 or 15(d)
                     of the Securities Exchange Act of 1934

        Date of Report (Date of earliest event reported): December 12, 1999

                            21st Century Telecom Group, Inc.
    ----------------------------------------------------------------------
             (Exact name of Registrant as specified in its charter)

                                    Illinois
    ----------------------------------------------------------------------
         (State or other jurisdiction of incorporation or organization)

                333-47235                             36-4076758
    -----------------------------         --------------------------------
        (Commission File Number)       (I.R.S. Employer Identification Number)

                               World Trade Center
                          350 North Orleans, Suite 600
                             Chicago, Illinois 60654
    ----------------------------------------------------------------------
               (Address of principal executive offices) (Zip Code)

                                 (312) 955-2100
    ----------------------------------------------------------------------
              (Registrant's telephone number, including area code)
Item 5.   Other Events.

          On December 12, 1999, 21st Century Telecom Group, Inc. (the "Company")
     entered  into an  Agreement  and Plan of Merger (the  "Merger  Agreement"),
     among RCN  Corporation  ("Parent"),  21st  Holding  Corp.,  a wholly  owned
     subsidiary of Parent  ("Sub"),  and providing  for the  acquisition  of the
     Company by Parent in a transaction structured as a merger (the "Merger") of
     Sub with and into the Company,  with the Company  surviving  the Merger and
     becoming a wholly owned subsidiary of Parent.

          Consummation of the Merger is subject to certain conditions, including
     the  expiration or earlier  termination  of any  applicable  waiting period
     under the Hart-Scott-Rodino  Antitrust Improvements Act of 1976 and receipt
     of required regulatory approvals.  In addition,  consummation of the Merger
     is subject to the receipt of tenders and consents  from holders of at least
     a majority of the Company's 12-1/4 Senior Discount Notes Due 2008 ("Notes")
     and the debt securities  underlying the Company's 13-3/4% Senior Cumulative
     Exchangeable Preferred Stock, $0.01 par value ("Exchangeable Preferred") to
     remove  certain  restrictive  covenants  applicable  thereto at a price not
     exceeding 101% of their accreted value, in the case of the Notes,  and 101%
     of  their  liquidation  preference,  in the  case  of the  debt  securities
     underlying the  Exchangeable  Preferred.  A copy of the Merger Agreement is
     filed herewith as Exhibit 2.1 and  incorporated  by reference  herein.  The
     description of certain terms of the Merger  Agreement set forth herein does
     not  purport  to be  complete  and  is  qualified  in its  entirety  by the
     provisions of the Merger Agreement.

          A copy of the Merger  Agreement  is filed  herewith as Exhibit 2.1 and
     incorporated by reference  herein.  The description of certain terms of the
     Merger  Agreement  set forth  herein does not purport to be complete and is
     qualified in its entirety by the provisions of the Merger Agreement.

Item 7.   Financial Statements and Exhibits.

     (c)  Exhibits.

         Exhibit No.

          2.1  Agreement and Plan of Merger, dated as of December 12, 1999,
               among RCN Corporation, 21st Holding Corp. and 21st Century
               Telecom Group, Inc.
SIGNATURES

     Pursuant to the  requirements  of the Securities  Exchange Act of 1934, the
Registrant  has duly  caused  this  report  to be  signed  on its  behalf by the
undersigned hereunto duly authorized.

                                               21st CENTURY TELECOM GROUP, INC.

         Dated: December 14, 1999                By: /s/  James K. Nugent
                                                     --------------------
                                                     James K. Nugent
                                                     Corporate Controller
21st CENTURY TELECOM GROUP, INC

                                    FORM 8-K

                                  EXHIBIT INDEX

         Exhibit No.

          2.1  Agreement and Plan of Merger, dated as of December 12, 1999,
               among RCN Corporation, 21st Holding Corp. and 21st Century
               Telecom Group, Inc.