Mixed gender onsens in Tokyo

I already noticed that most onsens have separated baths for males and females, so I was wondering which onsens in Tokyo have mixed gender baths. I will be on vacation with a girlfriend, so each bathing in different baths don't seem like too much fun to us.

And are swimming clothes allowed(or required) for mixed onsens?

Mixed gender onsens are relatively few and tend to be out in the countryside. These are almost all "no swimsuits". The overwhelming majority of onsens are separated and "no swimsuits", hence it is more of a group holiday activity than one for a couple on holiday by themselves.

The only mixed gender, swimsuits okay hot spring I have been to was on Izu Oshima, about a 3 hour ferry ride from Tokyo. I believe there is another one in Hakone, which is about 90 minutes out of Tokyo- I haven't been there so maybe someone else can help with details.

Patrick,

This has been asked and answered many times before here, so you should find details of other places by trawling back through the forum archives. One of the best swimsuit places closest to Tokyo is Yunessun in Hakone. Many proper onsen resorts and hotels also let you reserve an onsen privately for an hour or so, so that is another option.