IISExpress Log File Location

1 . By default applicationhost.config file defines following two log file locations. Here IIS_USER_HOME would be expanded as %userprofile%\documents\IISExpress\.

<siteDefaults>
<logFile logFormat="W3C" directory="%IIS_USER_HOME%\Logs" />
<traceFailedRequestsLogging directory="%IIS_USER_HOME%\TraceLogFiles" enabled="true" />
</siteDefaults>

You can update above directory paths to change the log file locations.

2 . If you are running IIS Express from command line, you can use '/config' switch to provide configuration file of your choice. Following link may help you http://learn.iis.net/page.aspx/870/running-iis-express-from-the-command-line/

By default it will be in:

C:\Users\ user_name \Documents\IISExpress\Logs\

http://www.iis.net/configreference/system.applicationhost/sites/sitedefaults

<configuration>
    <system.applicationHost>
       <sites>
          <siteDefaults>
             <logFile 
                logFormat="W3C"
                directory="%SystemDrive%\inetpub\logs\LogFiles"
                enabled="true" 
                />
             <traceFailedRequestsLogging 
                enabled="true"
                directory="%SystemDrive%\inetpub\logs\FailedReqLogFiles"
                maxLogFiles="20" 
                />
             <limits connectionTimeout="00:01:00" />
             <ftpServer serverAutoStart="true" />
             <bindings>
                <binding 
                    protocol="http" 
                    bindingInformation="127.0.0.1:8080:" 
                    />
             </bindings>
          </siteDefaults>
       </sites>
    </system.applicationHost>
</configuration>

I find web.config documentation is a messy. It is therefore better to provide a complete parent history than a floating snippet with the expectation that the reader naturally knows where it goes.