Lead paint can be on most any surface in older homes.  Homes built before 1978 are where lead is most commonly found.  Older houses have a higher chance than newer houses.  Typically lead paint is found on exterior parts of a house, including the siding, trim work, and windows. 

Many interior paints had lead in them too.  These were used mostly for trim work in rooms, closet parts, or in many places in kitchens and bathrooms.  Not just wood was painted with lead paint either, many metal and masonry surfaces may also be coated with lead paint.  Even varnishes and stains can contain lead!