AS OF MAY 2016, THIS PLUGIN IS NOT BEING MAINTAINED AND WILL NOT RECEIVE ANY FUTURE UPDATES. 
CONTACT ME IF YOU’D LIKE TO LIST AN ALTERNATIVE HERE.
Alternatives: 
– https://wordpress.org/plugins/footnotation/
This plugin provides an extremely easy way to add elegant looking footnotes to 
your posts. The syntax is natural, simple to understand, and degrades 
gracefully if the plugin is removed. Footnotes are linked unobtrusively and the 
note itself links back to the original text where the footnote is referenced.
Adding footnotes to a post is simple. Just type them inline in your post in 
square brackets like this:
<pre><code> [1. This is a footnote.]
</code></pre>
Each footnote must have a number followed by a period and a space and then the 
actual footnote. They don’t have to be unique but it is recommended. It doesn’t 
matter what the numbers are since the footnotes will be automatically 
renumbered when the post is displayed.
Footnotes can contain anything you’d like including links, images, etc. 
Footnotes are automatically linked back to the spot in the text where the note 
was made.
<h4>Settings</h4>
Only show footnotes on single post/page: This option will hide 
footnotes on the main blog page. Footnote numbers will still appear 
but link to the individual post/page URL.
Collapse footnotes until clicked: When checked, footnotes are 
hidden until manually expanded or a footnote number is clicked.
Note: Do not include square brackets [] inside the footnotes themselves.
Note: Footnote numbers don’t need to be unique but it is recommended, 
especially if the text is identical for multiple footnotes. If you have 
multiple footnotes with the exact same text and number then you’ll get weird 
and incorrect footnotes on your post.

FD Footnotes Plugin

Add elegant looking footnotes to your posts simply and naturally.

Heavy Heavy

Erik Ford

Endnotes is a simple solution for adding footnotes to your WordPress posts or pages. The plugin originated as a fork of John Watson’s FD <a href="https://wordpress.org/plugins/fd-footnotes/" rel="ugc">Footnotes</a> but has been updated to use the WordPress Settings API. The original plugin’s usage and functionality has been retained.
<h4>How to Use</h4>
You can add footnotes to your posts or pages by adding numbered inline content within square brackets. Place the inline content where you would like the superscript numeral to appear.
<pre><code>I am Jack's happy sentence that will contain a footnote[1. I am Jack's happy footnote] for calling out a reference.
</code></pre>
Each footnote must have a number, followed by a period and a space, and then the actual footnote. They don’t have to be unique but it is recommended. It doesn’t matter what the numbers are since the footnotes will be automatically renumbered when the post is displayed.
Footnotes can contain anything you’d like including links, images, etc. Footnotes are automatically linked back to the spot in the text where the note was made.
<h4>Square Bracket Usage</h4>
Do not include square brackets inside the footnotes themselves.
<h4>Unique Footnote Numbers</h4>
Footnote numbers don’t need to be unique but it is highly recommended, especially if the text is identical for multiple footnotes. If you have multiple footnotes with the exact same text and number, you may get undesirable results.

Endnotes

Easily add footnotes to your posts and pages.

FD Footnotes Plugin vs Endnotes