Downloading the official Facebook app for Android 2.1 (Eclair) is no longer possible through the Google Play Store, as modern versions require at least Android 6.0 (Marshmallow) or higher. 

How to download the Facebook app for Android 2.1 (Eclair) — what to know

Important upfront: Android 2.1 (Eclair) is very old (released 2010). Current Facebook app versions require much newer Android releases, so you cannot install the modern Facebook app from the Google Play Store on Android 2.1. Below are practical options and constraints.

Your Android 2.1 device is a piece of history. With this guide, you can keep it useful as a Facebook communicator for years to come. And when the legacy app finally refuses to connect, know that the tiny, text-based mobile website will always be there for you.

Install: Open your "Downloads" folder and tap the .apk file to begin the installation process. Better Alternatives for Older Devices

Where to Download: You can find these archived files on APKMirror. Installation: Go to Settings > Applications.

Downloading the Facebook app for Android 2.1 Eclair is a journey into mobile history. While modern versions of Facebook require at least Android 6.0, users with legacy hardware can still access the platform by using archived APK files or optimized mobile web interfaces. The Challenge: Android 2.1 Support Status