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https://{Your_Domain_URL}/services/data/v56.0/limits/recordCount can be used to find the number of records in each Salesforce Object using REST API.
Workbench:
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Postman Client:
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https://{Your_Domain_URL}/services/data/v56.0/limits/recordCount can be used to find the number of records in each Salesforce Object using REST API.
Workbench:
Postman Client: