Without even thinking about it, I typed my password into the Google search bar, but I didn't press enter. Since autocomplete is on, does that mean my password has been logged or indexed somewhere? Would it be a good idea to change my password or is that just being paranoid? 
I highly doubt it.


You didn't press enter but Google will sometimes send the information to quickly present your results. This is forced over HTTPS. Your information was likely encrypted and not exposed.
According to most sources Google processes on average 3.5 billion searches per day. There is no additional information to prove your query is a password. Nor is there any public way for a person to get the search queries of a particular Google user. So they would have to be an actual employee of Google. The likelihood of a internal Google employee to trying your search queries as passwords to your account is highly unlikely. It might not even be possible for most standard Google employees to get such identifying information. But if so, the possibility of one with such access purposely targeting you is astronomical.
Again, there is no additional context to prove it is your password. Nor is your user information submitted with your query. So in the event of a MITM attack where they can read your traffic I would still factor it as real low as they would also have to have your username.


I am going to flat out say there 99.9% chance you have nothing to worry about. If you are wearing a tin foil hat or still have a nervous tick then change your password. If you don't use this password elsewhere then you're golden since it isn't like they could log in with an old password. Otherwise I would move on and not worry about it.

Edit: @reirab made a point it could make it pop up in features that use your search history. I don't believe this happens if you don't press submit. But if you want to be sure clear your search history with Google. I can't be sure this clears it from Google's servers but it should prevent them from popping up in the auto-complete.
