Portland Water Bureau owns the main in the street and the section up to the meter — anything from the meter to your house belongs to you. On a typical Portland lot that's 50–75 feet, and on older inner-east-side properties (Irvington, Sellwood, Eastmoreland, Ladd's Addition) it's almost always still the original galvanized steel — the most common candidate for full replacement we see.
If you haven't yet had someone diagnose the line, replacement may not be the right answer. Many leaks on otherwise-sound runs are repairable in place, and we have a separate page for that scope. The page you're on is for homeowners who already know the line is past saving, or who'd rather replace once than chase repeat repairs.