If you use Windows open the task manager while chromium (or the program, that seems to be it) is open (using Ctrl-Alt-Del and clicking on Task-Manager).
Try to find in the tab processes a chromium.exe or chrome.exe and try to end process. Once it's done go to control panel and try uninstalling.

If this issue still persists let us know on which OS platform you are facing this issue?

Hi. Generally when we see reports of "I cannot uninstall Chromium", it is the result of some unwanted software that has force-installed Chromium on users' machines. If removing it via the "Programs and Features" control panel does not work, you could try finding and deleting the files (possibly in C:\Users\YOU\AppData\Local\Chromium\Application). You could also try running the Chrome Cleanup Tool (https://www.google.com/chrome/cleanup-tool/) to see if it finds any software that it suggests be removed.

Since Google Chrome is not involved, I am closing this issue for now. Please re-open if you are having trouble uninstalling "Google Chrome".