Not that it would give you 100% accuracy, but you can use hostip.info
They provide an API that gives you the location of an IP address that you pass them via HTTP request. You can use a WebClient object to make calls to the API and parse the results. Scott Hanselman has a pretty great example in this blog article (my example below is based on his article). hostip.info's database is based on an open project that the community contributes IP locations to... so there is no guarantee to be correct.
For starters, you need to determine the client IP address as follows:
string ipaddress = HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"];
Once you have the IP, you can create a WebClient object and call the API...
Example API call:
string r;
using (var w = new WebClient())
{
r = w.DownloadString(String.Format("http://api.hostip.info/?ip={0}&position=true", ipaddress));
}
The results will be XML that looks something like this:
<?xml version="1.0" encoding="ISO-8859-1" ?>
<HostipLookupResultSet version="1.0.0" xmlns="http://www.hostip.info/api" xmlns:gml="http://www.opengis.net/gml" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.hostip.info/api/hostip-1.0.0.xsd">
<gml:description>This is the Hostip Lookup Service</gml:description>
<gml:name>hostip</gml:name>
<gml:boundedBy>
<gml:Null>inapplicable</gml:Null>
</gml:boundedBy>
<gml:featureMember>
<Hostip>
<gml:name>Sugar Grove, IL</gml:name>
<countryName>UNITED STATES</countryName>
<countryAbbrev>US</countryAbbrev>
<!-- Co-ordinates are available as lng,lat -->
<ipLocation>
<gml:PointProperty>
<gml:Point srsName="http://www.opengis.net/gml/srs/epsg.xml#4326">
<gml:coordinates>-88.4588,41.7696</gml:coordinates>
</gml:Point>
</gml:PointProperty>
</ipLocation>
</Hostip>
</gml:featureMember>
</HostipLookupResultSet>
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