<TABLE> <S> <C>

<PAGE>
 
<ARTICLE> UT
<LEGEND> This schedule contains summary financial information extracted from the
Consolidated Balance Sheet and Statement of Consolidated Capitalization as of
March 31, 1998 and the related Statements of Consolidated Operations, Retained
Earnings (Deficit) and Cash Flows for the three months ended March 31, 1998 and
is qualified in its entirety by reference to such financial statements.
</LEGEND>
<CIK>      0000918040
<NAME>     UNICOM CORPORATION
<MULTIPLIER> 1,000
       
<S>                             <C>
<PERIOD-TYPE>                   3-MOS
<FISCAL-YEAR-END>                          DEC-31-1998
<PERIOD-START>                             JAN-01-1998
<PERIOD-END>                               MAR-31-1998
<BOOK-VALUE>                                  PER-BOOK 
<TOTAL-NET-UTILITY-PLANT>                   16,456,748
<OTHER-PROPERTY-AND-INVEST>                  2,368,395
<TOTAL-CURRENT-ASSETS>                       1,668,066
<TOTAL-DEFERRED-CHARGES>                             0<F1>
<OTHER-ASSETS>                               1,695,810
<TOTAL-ASSETS>                              22,189,019
<COMMON>                                     4,945,437
<CAPITAL-SURPLUS-PAID-IN>                            0
<RETAINED-EARNINGS>                           (54,207)
<TOTAL-COMMON-STOCKHOLDERS-EQ>               4,887,890<F2>
<PREFERRED-MANDATORY>                          174,328<F3>
<PREFERRED>                                    506,920<F3>
<LONG-TERM-DEBT-NET>                         5,757,279<F4>
<SHORT-TERM-NOTES>                                   0<F1>
<LONG-TERM-NOTES-PAYABLE>                            0<F4>
<COMMERCIAL-PAPER-OBLIGATIONS>                       0<F1>
<LONG-TERM-DEBT-CURRENT-PORT>                  139,413
<PREFERRED-STOCK-CURRENT>                       30,688<F3>
<CAPITAL-LEASE-OBLIGATIONS>                    424,343
<LEASES-CURRENT>                               240,895
<OTHER-ITEMS-CAPITAL-AND-LIAB>              10,027,263<F5>
<TOT-CAPITALIZATION-AND-LIAB>               22,189,019
<GROSS-OPERATING-REVENUE>                    1,712,235
<INCOME-TAX-EXPENSE>                            34,196<F6>
<OTHER-OPERATING-EXPENSES>                   1,477,430
<TOTAL-OPERATING-EXPENSES>                   1,521,821
<OPERATING-INCOME-LOSS>                        190,414
<OTHER-INCOME-NET>                            (28,331)<F6><F7>
<INCOME-BEFORE-INTEREST-EXPEN>                 172,278
<TOTAL-INTEREST-EXPENSE>                       118,563
<NET-INCOME>                                    53,715
<PREFERRED-STOCK-DIVIDENDS>                          0<F7>
<EARNINGS-AVAILABLE-FOR-COMM>                   53,715
<COMMON-STOCK-DIVIDENDS>                        86,739
<TOTAL-INTEREST-ON-BONDS>                            0<F8>
<CASH-FLOW-OPERATIONS>                         366,439
<EPS-PRIMARY>                                     0.25
<EPS-DILUTED>                                     0.25
<FN> 
<F1> This item is not disclosed as a separate line item on the Consolidated 
     Balance Sheet.
<F2> Includes a deduction of $3,340 thousand for preference stock expense of 
     ComEd.
<F3> Preferred and preference stocks of ComEd.
<F4> $1,023,954 thousand of notes and long-term note to bank is included in 
     LONG-TERM-DEBT-NET.
<F5> Includes $350,000 thousand of ComEd-obligated mandatorily redeemable
     preferred securities of subsidiary trusts holding solely ComEd's
     subordinated debt securities.
<F6> A tax benefit of $10,195 thousand related to nonoperating activities is
     included in INCOME-TAX-EXPENSE.
<F7> A $14,547 thousand provision for preferred and preference stock dividends
     of ComEd and a $7,428 thousand provision for preferred securities dividends
     of subsidiary trusts holding solely ComEd's subordinated debt securities
     are included in OTHER-INCOME-NET.
<F8> This item is not disclosed as a separate line item on the Statement of
     Consolidated Operations.
</FN>  
        

</TABLE>