The 31-year-old has joined the newly-promoted SPL side on a deal which will run until January.
Brown spent last season at Hibernian and had previous spells with Motherwell, Inverness and Celtic.
County boss Derek Adams said: "Mark is a talented and experienced player which is what we need at this stage.
"Michael Fraser has had a superb start to the season, with three clean-sheets already, but there is no doubt it was an area we needed to strengthen.
"Goalkeeper is such a crucial position in the team that attracting the right individuals, with top level experience, is always a challenge.
"I am therefore delighted that we've been able to secure Mark's services."
Chelsea won the Europa League on Wednesday. The Blues defeated Benfica 2-1 on injury time goal from Ivanovic.
The Liverpool 2013/14 soccer jersey is available for pre-order. The Reds are eager to compete for silver next season.
One of the top soccer cleats for control the Nike CTR360 will not let you down on the field in tight spaces.
adidas has added some color to the Predator line with this new colorway. Released on May 17. Be the first to own a pair.
The adidas Nitrocharge is the most talked about new cleat in years. It was released on May 15 and will take your pitch by storm.
The Juventus jersey for the 2013/14 was released earlier this week. Be the first to wear the colors of the Old Lady.
Bayern Munich are kings of Germany and hope to be crowned kings of Europe at Wembley later this month!
The push for more color on their cleats, adidas has added the infrared colorway to the adiZero f50 Line.
The new PUMA evoSPEED 1.2 FG. A great new soccer cleat with classic look and first time for PUMA to be on the cleat.
Borussia Dortmund hears Wembley Calling and are headed to London for the Champions League final.