She was elected at the POS annual general meeting in Nottingham last week and becomes its 23rd president since its formation in 1997.
A chartered town planner with a background covering development management and policy, Sarah leads the county council's strategic planning and infrastructure team.
At the meeting, Sarah said: "As public sector planners, we are often under-resourced, unseen and sometimes under-appreciated and yet each of us contributes daily to improving the lives of people in our community.
"I will be focusing this year’s presidency on the future – future leaders, future technology and future planners."
Platts replaces Paul Seddon, Nottingham City Council’s director of planning and regeneration.
The new senior vice-president is Richard Morris, chief planning officer at Sevenoaks District Council, while the new junior vice-president is Victoria Geoghegan, assistant director for planning and building control at the Royal Borough of Greenwich.
A summary of five key messages from last week's POS conference can be found here.