I don't think you're correct. Generally, if a Catholic marries outside the Church without a dispensation from the bishop, the marriage is invalid due to lack of form.
Here is an article that explains it better than I can:
http://www.catholiceducation.org/articles/religion/re0043.html
Here is a short quote from the article:
“However, if a Catholic enters marriage outside of the Catholic Church without the necessary dispensation, then the marriage is considered invalid and is not recognized by the Church. Moreover, this action places the person in a state of mortal sin. For instance, if a Catholic marrying either another Catholic or anyone else just decides to be married in some other Church or by a Justice of the Peace, that marriage is invalid. While such a marriage may have legal standing in the eyes of the state, it has no legitimate standing in the eyes of the Church.”
sitetest
I assumed proper form to go with proper ministers, but it is hard to ascertain proper form.
To your point, just going before a Justice of the Peace would obviously not have proper form.