Williams, who began his career at Newtown before returning to Latham Park after a brief stint at Aberystwyth Town - achieved the milestone on Friday evening as the Robins were held to a goalless draw against Cardiff Met.
Williams, who has missed a number of first team games this season, needs to make just 17 more Robins outing to surpass the all time record held by Colin Reynolds.
The former Caersws and Newtown man played 516 times in Wales’ top flight - and Williams looks set to take the crown with plans to continue for at least two more seasons.
“It makes me a very old man,” when asked about his 500th appearance.
“I didn’t know until before the game when it was tweeted out - but I am very proud of it.
“It is a big moment for myself and the club too, they have stuck with me through thick and thin, some good performances and not so good.
“I hope to have a couple more years left in me now.
“It is great to reach the milestone, and I hope to kick on.”