Google Tag Manager tag to load GeoIP data into the GTM data layer. Helps with GDPR.

gtm-maxmind-geoip2-tag.html

<script src="//js.maxmind.com/js/apis/geoip2/v2.1/geoip2.js"></script>
<script>

	/*
	 * get geographical location data by ip address
	 * uses the free ipify.org services
	 * and the paid Maxmind GeoIP2 Precision services
	 */

	(function (geoip2) {

		"use strict";

		// mark the start of the script loading
		var start = (new Date()).getTime();
		window.dataLayer = window.dataLayer || [];
		window.dataLayer.push({
			"event": "geoip.js",
			"geoip.start": start
		});
		triggerDOMEvent(document, "geoipjs", { "start": start });

		var isGeoIPLoaded, isWindowLoaded;

		function onWindowLoadAndGeoIPLoad () {

			if (isGeoIPLoaded && isWindowLoaded) {

				// push location data into GTM data layer
				window.dataLayer.push({
					"event": "geoip.window.load"
				});
				triggerDOMEvent(document, "geoipwindowload");

			}

		}

		// there is a possiblity that the document completes loading before now
		if (document.readyState === "complete") {

			isWindowLoaded = true;
			onWindowLoadAndGeoIPLoad();

		} else {

			window.addEventListener("load", function onWindowLoad () {

				isWindowLoaded = true;
				onWindowLoadAndGeoIPLoad();

			});

		}

		// helper function to push data to data layer
		function onSuccess (data, doNotSaveData) {

			// push location data into GTM data layer
			window.dataLayer.push({
				"event": "geoip.load",
				"geoip.data": data
			});
			triggerDOMEvent(document, "geoipload", data);
			isGeoIPLoaded = true;
			onWindowLoadAndGeoIPLoad();

			if (!doNotSaveData) {

				// store data in local storage
				if (data && data.traits && data.traits.ip_address) {

					var key = "maxmind.geoip2.data." + data.traits.ip_address;
					localStorage.setItem(key, JSON.stringify(data));

				}

			}

		}

		// helper function to log and throw error
		function onError (err) {

			throw new Error(err.code + ": " + err.error);

		}

		// helper function to execute once we have the IP address
		function onIPLoaded (ip) {

			window.dataLayer.push({
				"event": "geoip.ip",
				"geoip.ip": ip
			});
			triggerDOMEvent(document, "geoipip", { "ip": ip });

			// check local storage for geoip data for that IP address
			var key = "maxmind.geoip2.data." + ip;
			var data = localStorage.getItem(key);
			if (data) {

				// GeoIP data found in local storage
				try {
					data = JSON.parse(data);
					onSuccess(data, true);
				} catch (err) {
					throw err;
				}

			} else {

				// fetch GeoIP data from Maxmind
				geoip2.country(onSuccess, onError);

			}

		}

		var ip = sessionStorage.getItem("ipify.ip");
		if (ip) {

			// use IP address retrived from session cache
			onIPLoaded(ip);

		} else {

			// use ipify.org to get IP address
			// listen for when the IP address has been loaded by ipfiy
			window.ipifyCallback = function ipifyCallback (json) {

				sessionStorage.setItem("ipify.ip", json.ip);
				onIPLoaded(json.ip);

			};

			// inject the script from ipify.org
			var newNode, referenceNode;

			referenceNode = document.getElementsByTagName("script")[0];
			newNode = document.createElement("script");
			newNode.async = true;
			newNode.src = "https://api.ipify.org?format=jsonp&callback=ipifyCallback";
			referenceNode.parentNode.insertBefore(newNode, referenceNode);

		}

		// helper function to trigger native DOM events
		function triggerDOMEvent (element, type, detail, bubbles, cancelable) {

			// defaults
			if (!(element instanceof EventTarget)) {
				throw new Error("First argument, element, must be an instance of EventTarget.");
			}
			bubbles = bubbles || false;
			cancelable = cancelable || false;

			var event;

			if (CustomEvent) {

				// the modern way
				event = new CustomEvent(type, {
					"bubbles": bubbles,
					"cancelable": cancelable,
					"detail": detail
				});

			} else {

				// the old fashioned way to support Internet Explorer
				event = document.createEvent("Event");
				event.initEvent(type, bubbles, cancelable, detail);

			}

			// be nice and set the current target
			event.currentTarget = element;

			// target can be any Element or other EventTarget.
			element.dispatchEvent(event);

		}

	}(window.geoip2));

</script>

Updated with code to trigger events on the DOM as well as in GTM.