About nine caravans and 14 cars have pitched up in Royston Town Hall carpark as travellers, with about 40 children, settled in.
Police were informed on Friday evening that travellers were moving into the town hall car park and officers attended the scene and have continued to monitor the situation.
The occupants have been issued with a code of conduct, which sets out ground rules regarding acceptable behaviour.
Officers are working in partnership with North Herts District Council, which owns the land, to resolve the situation.
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