I would use a web service that can return JSON (along with jQuery to make things simpler). Below are all the free active IP lookup services I could find and the information they return. If you know of any more, then please add a comment and I'll update this answer.

---

DB-IP

Try it: http://api.db-ip.com/addrinfo?api_key=<your api key>&addr=<ip address>

Returns:

{
  "address": "116.12.250.1",
  "country": "SG",
  "stateprov": "Central Singapore",
  "city": "Singapore"
}

Limitations:

• 2,500 requests per day
• Doesn't support JSONP callbacks
• Requires IP address parameter
• Requires an email address to get your API key
• No SSL (https) with the free plan

---

Geobytes

Try it: http://gd.geobytes.com/GetCityDetails

$.getJSON('http://gd.geobytes.com/GetCityDetails?callback=?', function(data) {
  console.log(JSON.stringify(data, null, 2));
});

Returns:

{
  "geobytesforwarderfor": "",
  "geobytesremoteip": "116.12.250.1",
  "geobytesipaddress": "116.12.250.1",
  "geobytescertainty": "99",
  "geobytesinternet": "SA",
  "geobytescountry": "Saudi Arabia",
  "geobytesregionlocationcode": "SASH",
  "geobytesregion": "Ash Sharqiyah",
  "geobytescode": "SH",
  "geobyteslocationcode": "SASHJUBA",
  "geobytescity": "Jubail",
  "geobytescityid": "13793",
  "geobytesfqcn": "Jubail, SH, Saudi Arabia",
  "geobyteslatitude": "27.004999",
  "geobyteslongitude": "49.660999",
  "geobytescapital": "Riyadh ",
  "geobytestimezone": "+03:00",
  "geobytesnationalitysingular": "Saudi Arabian ",
  "geobytespopulation": "22757092",
  "geobytesnationalityplural": "Saudis",
  "geobytesmapreference": "Middle East ",
  "geobytescurrency": "Saudi Riyal",
  "geobytescurrencycode": "SAR",
  "geobytestitle": "Saudi Arabia"
}

Limitations:

• 16,384 requests per hour
• No SSL (https) with the free plan
• Can return the wrong location (I'm in Singapore, not Saudi Arabia)

---

GeoIPLookup.io

Try it: https://json.geoiplookup.io/api

$.getJSON('https://json.geoiplookup.io/api?callback=?', function(data) {
  console.log(JSON.stringify(data, null, 2));
});

Returns:

{
    "ip": "116.12.250.1",
    "isp": "SGPOST",
    "org": "Singapore Post Ltd",
    "hostname": "116.12.250.1",
    "longitude": "103.807",
    "latitude": "1.29209",
    "postal_code": "",
    "city": "Singapore",
    "country_code": "SG",
    "country_name": "Singapore",
    "continent_code": "AS",
    "region": "Central Singapore",
    "district": "",
    "timezone_name": "Asia\/Singapore",
    "connection_type": "",
    "asn": "AS3758 SingNet",
    "currency_code": "SGD",
    "currency_name": "Singapore Dollar",
    "success": true
}

Limitations:

• Unknown

---

geoPlugin

Try it: http://www.geoplugin.net/json.gp

$.getJSON('http://www.geoplugin.net/json.gp?jsoncallback=?', function(data) {
  console.log(JSON.stringify(data, null, 2));
});

Returns:

{
  "geoplugin_request": "116.12.250.1",
  "geoplugin_status": 200,
  "geoplugin_credit": "Some of the returned data includes GeoLite data created by MaxMind, available from <a href=\\'http://www.maxmind.com\\'>http://www.maxmind.com</a>.",
  "geoplugin_city": "Singapore",
  "geoplugin_region": "Singapore (general)",
  "geoplugin_areaCode": "0",
  "geoplugin_dmaCode": "0",
  "geoplugin_countryCode": "SG",
  "geoplugin_countryName": "Singapore",
  "geoplugin_continentCode": "AS",
  "geoplugin_latitude": "1.2931",
  "geoplugin_longitude": "103.855797",
  "geoplugin_regionCode": "00",
  "geoplugin_regionName": "Singapore (general)",
  "geoplugin_currencyCode": "SGD",
  "geoplugin_currencySymbol": "&#36;",
  "geoplugin_currencySymbol_UTF8": "$",
  "geoplugin_currencyConverter": 1.4239
}

Limitations:

• 120 requests per minute
• No SSL (https) with the free plan

---

Hacker Target

Try it: https://api.hackertarget.com/geoip/?q=<ip address>

Returns:

IP Address: 116.12.250.1
Country: SG
State: N/A
City: Singapore
Latitude: 1.293100
Longitude: 103.855797

Limitations:

• 50 requests per day
• Doesn't support JSONP callbacks
• Requires IP address parameter
• Returns plain text

---

ipapi.co

Try it: https://ipapi.co/json/

$.getJSON('https://ipapi.co/json/', function(data) {
  console.log(JSON.stringify(data, null, 2));
});

Returns:

{
  "ip": "116.12.250.1",
  "city": "Singapore",
  "region": "Central Singapore Community Development Council",
  "country": "SG",
  "country_name": "Singapore",
  "postal": null,
  "latitude": 1.2855,
  "longitude": 103.8565,
  "timezone": "Asia/Singapore"
}

Limitations:

• 1,000 requests per day
• Requires SSL (https)

---

IP-API.com

Try it: http://ip-api.com/json

$.getJSON('http://ip-api.com/json?callback=?', function(data) {
  console.log(JSON.stringify(data, null, 2));
});

Returns:

{
  "as": "AS3758 SingNet",
  "city": "Singapore",
  "country": "Singapore",
  "countryCode": "SG",
  "isp": "SingNet Pte Ltd",
  "lat": 1.2931,
  "lon": 103.8558,
  "org": "Singapore Telecommunications",
  "query": "116.12.250.1",
  "region": "01",
  "regionName": "Central Singapore Community Development Council",
  "status": "success",
  "timezone": "Asia/Singapore",
  "zip": ""
}

Limitations:

• 150 requests per minute
• No SSL (https) with the free plan

---

Ipdata.co

Try it: https://api.ipdata.co

$.getJSON('https://api.ipdata.co', function(data) {
  console.log(JSON.stringify(data, null, 2));
});

Returns:

{
  "ip": "116.12.250.1",
  "city": "Singapore",
  "region": "Central Singapore Community Development Council",
  "region_code": "01",
  "country_name": "Singapore",
  "country_code": "SG",
  "continent_name": "Asia",
  "continent_code": "AS",
  "latitude": 1.2931,
  "longitude": 103.8558,
  "asn": "AS3758",
  "organisation": "SingNet",
  "postal": "",
  "calling_code": "65",
  "flag": "https://ipdata.co/flags/sg.png",
  "emoji_flag": "\ud83c\uddf8\ud83c\uddec",
  "emoji_unicode": "U+1F1F8 U+1F1EC",
  "is_eu": false,
  "languages": [
    {
      "name": "English",
      "native": "English"
    },
    {
      "name": "Malay",
      "native": "Bahasa Melayu"
    },
    {
      "name": "Tamil",
      "native": "\u0ba4\u0bae\u0bbf\u0bb4\u0bcd"
    },
    {
      "name": "Chinese",
      "native": "\u4e2d\u6587"
    }
  ],
  "currency": {
    "name": "Singapore Dollar",
    "code": "SGD",
    "symbol": "S$",
    "native": "$",
    "plural": "Singapore dollars"
  },
  "time_zone": {
    "name": "Asia/Singapore",
    "abbr": "+08",
    "offset": "+0800",
    "is_dst": false,
    "current_time": "2018-05-09T12:28:49.183674+08:00"
  },
  "threat": {
    "is_tor": false,
    "is_proxy": false,
    "is_anonymous": false,
    "is_known_attacker": false,
    "is_known_abuser": false,
    "is_threat": false,
    "is_bogon": false
  }
}

Limitations:

• 1,500 requests per day
• Requires an email address to get your API key
• Requires SSL (https)

---

IP Find

Try it: https://ipfind.co/me?auth=<your api key>

$.getJSON('https://ipfind.co/me?auth=<your_api_key>', function(data) {
  console.log(JSON.stringify(data, null, 2));
});

Returns:

{
  "ip_address": "116.12.250.1",
  "country": "Singapore",
  "country_code": "SG",
  "continent": "Asia",
  "continent_code": "AS",
  "city": "Singapore",
  "county": null,
  "region": "Central Singapore",
  "region_code": "01",
  "timezone": "Asia/Singapore",
  "owner": null,
  "longitude": 103.8565,
  "latitude": 1.2855,
  "currency": "SGD",
  "languages": [
    "cmn",
    "en-SG",
    "ms-SG",
    "ta-SG",
    "zh-SG"
  ]
}

Limitations:

• 300 requests per day
• Requires registration to get your API key

---

ipgeolocation

Try it: https://api.ipgeolocation.io/ipgeo?apiKey=<your api key>

$.getJSON('https://api.ipgeolocation.io/ipgeo?apiKey=<your_api_key>', function(data) {
  console.log(JSON.stringify(data, null, 2));
});

Returns:

{
  "ip": "116.12.250.1",
  "continent_code": "AS",
  "continent_name": "Asia",
  "country_code2": "SG",
  "country_code3": "SGP",
  "country_name": "Singapore",
  "country_capital": "Singapore",
  "state_prov": "Central Singapore",
  "district": "",
  "city": "Singapore",
  "zipcode": "",
  "latitude": "1.29209",
  "longitude": "103.807",
  "is_eu": false,
  "calling_code": "+65",
  "country_tld": ".sg",
  "languages": "cmn,en-SG,ms-SG,ta-SG,zh-SG",
  "country_flag": "https://ipgeolocation.io/static/flags/sg_64.png",
  "isp": "SGPOST",
  "connection_type": "",
  "organization": "Singapore Post Ltd",
  "geoname_id": "1880252",
  "currency": {
    "name": "Dollar",
    "code": "SGD"
  },
  "time_zone": {
    "name": "Asia/Singapore",
    "offset": 8,
    "is_dst": false,
    "current_time": "2018-06-12 09:06:49.028+0800"
  }
}

Limitations:

• 50,000 requests per month
• Requires registration to get your API key

---

ipify

Try it: https://api.ipify.org/?format=json

$.getJSON('https://api.ipify.org?format=jsonp&callback=?', function(data) {
  console.log(JSON.stringify(data, null, 2));
});

Returns:

{
  "ip": "116.12.250.1"
}

Limitations:

• None

---

IPInfoDB

Try it: https://api.ipinfodb.com/v3/ip-city/?key=<your api key>&format=json

$.getJSON('https://api.ipinfodb.com/v3/ip-city/?key=<your_api_key>&format=json&callback=?', function(data) {
  console.log(JSON.stringify(data, null, 2));
});

Returns:

{
  "statusCode": "OK",
  "statusMessage": "",
  "ipAddress": "116.12.250.1",
  "countryCode": "SG",
  "countryName": "Singapore",
  "regionName": "Singapore",
  "cityName": "Singapore",
  "zipCode": "048941",
  "latitude": "1.28967",
  "longitude": "103.85",
  "timeZone": "+08:00"
}

Limitations:

• Two requests per second
• Requires registration to get your API key

---

ipinfo.io

Try it: https://ipinfo.io/json

$.getJSON('https://ipinfo.io/json', function(data) {
  console.log(JSON.stringify(data, null, 2));
});

Returns:

{
  "ip": "116.12.250.1",
  "hostname": "No Hostname",
  "city": "Singapore",
  "region": "Central Singapore Community Development Council",
  "country": "SG",
  "loc": "1.2931,103.8558",
  "org": "AS3758 SingNet"
}

Limitations:

• 1,000 requests per day

---

ipstack (formerly freegeoip.net)

Try it: http://api.ipstack.com/<ip address>?access_key=<your api key>

$.getJSON('http://api.ipstack.com/<ip_address>?access_key=<your_api_key>', function(data) {
  console.log(JSON.stringify(data, null, 2));
});

Returns:

{
    "ip": "116.12.250.1",
    "type": "ipv4",
    "continent_code": "AS",
    "continent_name": "Asia",
    "country_code": "SG",
    "country_name": "Singapore",
    "region_code": "01",
    "region_name": "Central Singapore Community Development Council",
    "city": "Singapore",
    "zip": null,
    "latitude": 1.2931,
    "longitude": 103.8558,
    "location": {
        "geoname_id": 1880252,
        "capital": "Singapore",
        "languages": [{
            "code": "en",
            "name": "English",
            "native": "English"
        },
        {
            "code": "ms",
            "name": "Malay",
            "native": "Bahasa Melayu"
        },
        {
            "code": "ta",
            "name": "Tamil",
            "native": "\u0ba4\u0bae\u0bbf\u0bb4\u0bcd"
        },
        {
            "code": "zh",
            "name": "Chinese",
            "native": "\u4e2d\u6587"
        }],
        "country_flag": "http:\/\/assets.ipstack.com\/flags\/sg.svg",
        "country_flag_emoji": "\ud83c\uddf8\ud83c\uddec",
        "country_flag_emoji_unicode": "U+1F1F8 U+1F1EC",
        "calling_code": "65",
        "is_eu": false
    }
}

Limitations:

• 10,000 requests per month
• Requires IP address parameter
• Requires registration to get your API key
• No SSL (https) with the free plan

---

jsonip.com

Try it: https://jsonip.com

$.getJSON('https://jsonip.com/?callback=?', function(data) {
  console.log(JSON.stringify(data, null, 2));
});

Returns:

{
  "ip": "116.12.250.1",
  "about": "/about",
  "Pro!": "http://getjsonip.com",
  "reject-fascism": "Liberal America will prevail"
}

Limitations:

• The response includes upsell and politics

---

JSON Test

Try it: http://ip.jsontest.com/

$.getJSON('http://ip.jsontest.com/?callback=?', function(data) {
  console.log(JSON.stringify(data, null, 2));
});

Returns:

{
  "ip": "116.12.250.1"
}

Limitations:

• No SSL (https)
• Goes down a lot (over quota), so I wouldn't use it for production
• Returns IPv6 address if you have one, which may not be what you want

---

Nekudo

Try it: https://geoip.nekudo.com/api

$.getJSON('https://geoip.nekudo.com/api', function(data) {
  console.log(JSON.stringify(data, null, 2));
});

Returns:

{
  "city": "Singapore",
  "country": {
    "name": "Singapore",
    "code": "SG"
  },
  "location": {
    "accuracy_radius": 50,
    "latitude": 1.2855,
    "longitude": 103.8565,
    "time_zone": "Asia/Singapore"
  },
  "ip": "116.12.250.1"
}

Limitations:

• Blocked by ad blockers using the EasyPrivacy list

---

Stupid Web Tools

Try it: http://www.stupidwebtools.com/api/my_ip.json

$.getJSON('http://www.stupidwebtools.com/api/my_ip.json', function(data) {
  console.log(JSON.stringify(data, null, 2));
});

Returns:

{
  "my_ip": {
    "ip": "116.12.250.1",
    "others": []
  }
}

Limitations:

• No SSL (https)

---

Keep in mind that since these are all free services, your mileage may vary in terms of exceeding quota and uptime, and who knows when/if they will be taken offline down the road (exhibit A: Telize). Most of these services also offer a paid tier in case you want more features like SSL support.

Also, as skobaljic noted in the comments below, the request quotas are mostly academic since this is happening client-side and most end users will never exceed the quota.

UPDATES

• 2/1/2016: Removed Telize (no longer offers free plan)
• 4/18/2016: Removed freegeoip.net (out of service)
• 4/26/2016: Added DB-IP
• 4/26/2016: Added Hacker Target
• 7/6/2016: Reinstated freegeoip.net
• 7/6/2016: Removed ip-json.rhcloud.com (dead link)
• 12/21/2016: Removed Hacker Target (out of service)
• 2/10/2017: Added Nekudo
• 4/20/2017: Added ipapi.co (thanks Ahmad Awais)
• 4/24/2017: Reinstated Hacker Target
• 4/24/2017: Removed Snoopi.io (out of service)
• 7/16/2017: Added IP Find (thanks JordanC)
• 7/16/2017: Updated limitation for free plans that don't support SSL
• 9/25/2017: Added Stupid Web Tools (thanks Cœur)
• 3/16/2018: Added Ipdata.co (thanks Jonathan)
• 4/14/2018: Renamed freegeoip.net to ipstack (thanks MA-Maddin)
• 4/16/2018: Added GeoIPLookup.io (thanks Rob Waa)
• 6/11/2018: Added ipgeolocation (thanks Ejaz Ahmed)