In the season 1 episode "Out of the Past" we're treated to a vision of Aang's adulthood. Toph Beifong is now the chief of police in Republic City (and looks very good for 40 years old). She helps Aang arrest a criminal mob boss named Yakone and bring him to trial, but his psychic Bloodbending abilities force her to release him.
This is sadly the only time we've seen Toph from this time period in the show so far. Here's hoping we'll get some more glimpses into the past and see more of her crime-fighting days.