diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3d0de88e60..153e4e21af 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -21,6 +21,7 @@ This change log adheres to standards from [Keep a CHANGELOG](http://keepachangel
 * [`jsx-handler-names`]: false positive when handler name begins with number ([#1689][] @jsphstls)
 * [`prop-types`]: Detect JSX returned by sequential expression ([#2801][] @mikol)
 * [`jsx-props-no-multi-spaces`]: "Expected no line gap between" false positive ([#2792][] @karolina-benitez)
+* [`no-unknown-property`]: check attributes with any input case ([#2790][] @julienw)
 
 ### Changed
 * [Tests] [`jsx-one-expression-per-line`]: add passing tests ([#2799][] @TaLeaMonet)
@@ -30,6 +31,7 @@ This change log adheres to standards from [Keep a CHANGELOG](http://keepachangel
 [#2796]: https://github.com/yannickcr/eslint-plugin-react/pull/2796
 [#2792]: https://github.com/yannickcr/eslint-plugin-react/pull/2792
 [#2791]: https://github.com/yannickcr/eslint-plugin-react/pull/2791
+[#2790]: https://github.com/yannickcr/eslint-plugin-react/pull/2790
 [#2789]: https://github.com/yannickcr/eslint-plugin-react/pull/2789
 [#2782]: https://github.com/yannickcr/eslint-plugin-react/pull/2782
 [#2780]: https://github.com/yannickcr/eslint-plugin-react/pull/2780
diff --git a/lib/rules/no-unknown-property.js b/lib/rules/no-unknown-property.js
index 18634951c3..352c8e24e1 100644
--- a/lib/rules/no-unknown-property.js
+++ b/lib/rules/no-unknown-property.js
@@ -147,7 +147,8 @@ function getDOMPropertyNames(context) {
 // ------------------------------------------------------------------------------
 
 /**
- * Checks if a node matches the JSX tag convention.
+ * Checks if a node matches the JSX tag convention. This also checks if a node
+ * is extended as a webcomponent using the attribute "is".
  * @param {Object} node - JSX element being tested.
  * @returns {boolean} Whether or not the node name match the JSX tag convention.
  */
@@ -194,7 +195,7 @@ function tagNameHasDot(node) {
  * Get the standard name of the attribute.
  * @param {String} name - Name of the attribute.
  * @param {String} context - eslint context
- * @returns {String} The standard name of the attribute.
+ * @returns {String | undefined} The standard name of the attribute, or undefined if no standard name was found.
  */
 function getStandardName(name, context) {
   if (DOM_ATTRIBUTE_NAMES[name]) {
@@ -203,13 +204,9 @@ function getStandardName(name, context) {
   if (SVGDOM_ATTRIBUTE_NAMES[name]) {
     return SVGDOM_ATTRIBUTE_NAMES[name];
   }
-  let i = -1;
   const names = getDOMPropertyNames(context);
-  const found = names.some((element, index) => {
-    i = index;
-    return element.toLowerCase() === name;
-  });
-  return found ? names[i] : null;
+  // Let's find a possible attribute match with a case-insensitive search.
+  return names.find((element) => element.toLowerCase() === name.toLowerCase());
 }
 
 // ------------------------------------------------------------------------------
@@ -259,6 +256,8 @@ module.exports = {
         }
 
         const tagName = getTagName(node);
+
+        // 1. Some attributes are allowed on some tags only.
         const allowedTags = ATTRIBUTE_TAGS_MAP[name];
         if (tagName && allowedTags && /[^A-Z]/.test(tagName.charAt(0)) && allowedTags.indexOf(tagName) === -1) {
           context.report({
@@ -272,8 +271,12 @@ module.exports = {
           });
         }
 
+        // 2. Otherwise, we'll try to find if the attribute is a close version
+        // of what we should normally have with React. If yes, we'll report an
+        // error. We don't want to report if the input attribute name is the
+        // standard name though!
         const standardName = getStandardName(name, context);
-        if (!isTagName(node) || !standardName) {
+        if (!isTagName(node) || !standardName || standardName === name) {
           return;
         }
         context.report({
diff --git a/tests/lib/rules/no-unknown-property.js b/tests/lib/rules/no-unknown-property.js
index 21197a4e06..5d9effecfa 100644
--- a/tests/lib/rules/no-unknown-property.js
+++ b/tests/lib/rules/no-unknown-property.js
@@ -37,6 +37,7 @@ ruleTester.run('no-unknown-property', rule, {
     {code: '<App xlink:href="bar" />;'},
     {code: '<App clip-path="bar" />;'},
     {code: '<div className="bar"></div>;'},
+    {code: '<div onMouseDown={this._onMouseDown}></div>;'},
     {code: '<div data-foo="bar"></div>;'},
     {code: '<div class="foo" is="my-elem"></div>;'},
     {code: '<div {...this.props} class="foo" is="my-elem"></div>;'},
@@ -75,6 +76,10 @@ ruleTester.run('no-unknown-property', rule, {
     code: '<div onmousedown="bar"></div>;',
     output: '<div onMouseDown="bar"></div>;',
     errors: [{message: 'Unknown property \'onmousedown\' found, use \'onMouseDown\' instead'}]
+  }, {
+    code: '<div onMousedown="bar"></div>;',
+    output: '<div onMouseDown="bar"></div>;',
+    errors: [{message: 'Unknown property \'onMousedown\' found, use \'onMouseDown\' instead'}]
   }, {
     code: '<use xlink:href="bar" />;',
     output: '<use xlinkHref="bar" />;',