# Exhibit 31.1

# Certification of the
Chairman and Chief Executive Officer of Alliant Energy
Corporation

I, Erroll B. Davis,
Jr., certify that:

|1. | I have reviewed this quarterly report on Form 10-Q of Alliant Energy
          Corporation;
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|2. | Based on my knowledge, this report does not contain any untrue statement of a
          material fact or omit to state a material fact necessary to make the statements
          made, in light of the circumstances under which such statements were made, not
          misleading with respect to the period covered by this report;
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|3. | Based on my knowledge, the financial statements, and other financial information
          included in this report, fairly present in all material respects the financial
          condition, results of operations and cash flows of the registrant as of, and
          for, the periods presented in this report;
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|4. | The registrants other certifying officer(s) and I are responsible for
          establishing and maintaining disclosure controls and procedures (as defined in
          Exchange Act Rules 13a-15(e) and 15d-15(e)) for the registrant and have:
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|a) |  | Designed
such disclosure controls and procedures, or caused such disclosure
               controls and procedures to be designed under our supervision, to ensure
that                material information relating to the registrant, including its
consolidated                subsidiaries, is made known to us by others within those
entities, particularly                during the period in which this report is being
prepared;
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|b) |  | Evaluated
the effectiveness of the registrants disclosure controls and
               procedures and presented in this report our conclusions about the
effectiveness                of the disclosure controls and procedures, as of the end of
the period covered                by this report based on such evaluation; and
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|c) |  | Disclosed
in this report any change in the registrants internal control                over
financial reporting that occurred during the registrants most recent
               fiscal quarter (the registrants fourth fiscal quarter in the case of
an                annual report) that has materially affected, or is reasonably likely to
               materially affect, the registrants internal control over financial
               reporting; and
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|5. | The registrants other certifying officer(s) and I have disclosed, based on
          our most recent evaluation of internal control over financial reporting, to the
          registrants auditors and the audit committee of the registrants
          board of directors (or persons performing the equivalent functions):
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|a) |  | All
significant deficiencies and material weaknesses in the design or operation
               of internal control over financial reporting which are reasonably likely
to                adversely affect the registrants ability to record, process,
summarize and                report financial information; and
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|b) |  | Any
fraud, whether or not material, that involves management or other employees
               who have a significant role in the registrants internal control over
               financial reporting.
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Date:  August 6, 2004

| | /s/ Erroll B. Davis, Jr.
| | ------------------------
| | Erroll B. Davis, Jr.    
| | Chairman and            
| | Chief Executive Officer