wooassist

This plugin adds a custom field in the checkout page to ask your customers where they heard about your store.
This plugin also offers an “Other” field where your customer can provide a specific answer in a separate textbox.
Features:
<ul>
<li>Easily change the labels and choices for the custom field in the checkout page.</li>
<li>View reports on the “Reports” section in WooCommerce.</li>
<li>Enable/disable the custom field to be required on checkout.</li>
<li>Enable/disable the “Other” field.</li>
<li>Modify order statuses you want to include in the reports.</li>
<li>Export Orders with Customer Source field</li>
</ul>

Where Did You Hear About Us Checkout Field for WooCommerce

Adds a custom field in the checkout page to ask your customers where they've heard about your store.

Automattic

WooCommerce

WooThemes

James Koster

A simple plugin that adds a full width widget region above the default, columnised Storefront footer widget area. Customise the display by adding a background image and tweaking colors via the Customizer.
This plugin requires the Storefront theme to be installed.

Storefront Footer Bar

Add a full width widgetised region above the default Storefront footer widget area.

Where Did You Hear About Us Checkout Field for WooCommerce vs Storefront Footer Bar