The definition of our Solar System has been getting changed in the 33 years of Voyager 1 & 2(1977). Obviously, at the time of their launch, most people and even many scientists would have put the boundary of the Solar System at the outermost planet, Pluto. Voyager 1 passed Pluto's orbit in May 1988 while Voyager 2 in August 1990. So you are correct in that milestone,
Now Pluto, even though it has been discovered to have a moon, has been demoted to a new category of 'dwarf planet' and now the furthest out is the similarly classified Eris. Recently discovered in 2005 at a current 3 times the distance of Pluto from the Sun or aphelion(max distance) of 97.5 AU (Astronomical Units, 1 AU is 93 million miles = Earth's orbit) to perihelion (min distance) of 37.7 AU (inside Pluto's aphelion.)
Voyager 1 is now at better than 120 AU while Voyager 2 is only[!] at 98 AU. So it is accurate only to say that Voyager 1 is well beyond the furthest discovered solid planet-like object (subject to change at any time!)