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                                                                   EXHIBIT 10.10
 
                              AMENDMENT NO. 1 TO
                  EXECUTIVE EMPLOYMENT AGREEMENT AND CONSENT
                  ------------------------------------------


     This Amendment No. 1 to Executive Employment Agreement and Consent (this
"Amendment") is entered into as of this 21st day of August, 1998, between Focal
Communications Corporation, a Delaware corporation (the "Company"), Renee M.
Martin ("Executive"), and Madison Dearborn Capital Partners, L.P., Frontenac VI,
L.P. and Battery Ventures III, L.P. (collectively, the "Stockholders").
Capitalized terms not otherwise defined in this Agreement are used herein with
the meanings assigned to such terms in the Stock Purchase Agreement, dated
November 27, 1996, by and among the Company and the other parties thereto (as
amended, the "Stock Purchase Agreement") or the Executive Employment Agreement
(as hereinafter defined), as the case may be.

     WHEREAS, the Company and the Executive wish to amend the provisions of the
Executive Employment Agreement, dated as of March 20, 1998, by and between the
Company and the Executive (the "Executive Employment Agreement") as provided in
paragraph 1 of this Amendment;

     WHEREAS, the Stockholders collectively own all of the Institutional
Investor Stock; and

     WHEREAS, the Stockholders wish to consent to the amendment (as provided in
paragraph 1 of this Amendment) for purposes of the Stock Purchase Agreement;

     NOW, THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which is hereby acknowledged, the parties to this Amendment
hereby agree as follows:

     1.  Amendment to Executive Employment Agreement.  Pursuant to paragraph
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5(g) of the Executive Employment Agreement, the definition of "Noncompete
Compensation" set forth in the fourth sentence of paragraph 3(c) of the
Executive Employment Agreement is hereby amended and restated to read in its
entirety as follows:

         "Noncompete Compensation" shall consist of 100% of the
         salary that Executive received under paragraph 1(d)
         above as compensation from the Company and its
         Subsidiaries immediately prior to Termination
         (Executive's "Previous Salary") together with the
         continuation of the medical benefits that the Company
         provided to Executive immediately prior to Termination
         (Executive's "Previous Benefits"); provided that if at
         any time during the Noncompetition Period Executive
         obtains other employment (i) with comparable medical
         benefits to Executive's Previous Benefits, Executive's
         Noncompete Compensation shall during the period of such
         employment not include the continued provision of
         medical benefits, and (ii) with a salary exceeding 100%
         of Executive's Previous Salary, Executive's Noncompete
         Compensation shall during the period of such
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         employment be reduced (but not below zero) by the amount
         of such excess."

     2.  Consent.  For all purposes of the Stock Purchase Agreement (including,
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without limitation, Section 4C(xii) thereof), each of the Stockholders consents
to the amendment set forth in paragraph 1 of this Amendment.

     3.  Counterparts.  This Amendment may be executed in multiple counterparts,
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each of which shall be an original and all of which taken together shall
constitute one and the same agreement.

     4.  Descriptive Headings.  The descriptive headings of this Amendment are
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inserted for convenience only and do not constitute a part of this Amendment.


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     IN WITNESS WHEREOF, the parties hereto have executed this Amendment as of
the date first above written.


                           _____________________________________________________
                           Renee M. Martin


                           FOCAL COMMUNICATIONS CORPORATION

                           By:__________________________________________________
                                Its:____________________________________________

                           MADISON DEARBORN CAPITAL
                           PARTNERS, L.P.
                           By: Madison Dearborn Partners, L.P., its General
                               Partner
                           By: Madison Dearborn Partners, Inc., its General
                               Partner

                           By:__________________________________________________
                                Its:____________________________________________


                           FRONTENAC VI, L.P.
                           By:  Frontenac Company, its General Partner

                           By:__________________________________________________
                                Its:____________________________________________


                           BATTERY VENTURES III, L.P.
                           By:  Battery Partners III, L.P., its General Partner

                           By:__________________________________________________
                                Its:____________________________________________

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