How many campaign members are associated with a campaign?

From the Campaigns List page, you can drill down into each campaign record to view campaign members that have responded to a given campaign.

You can also access the Campaign Members report that shows the amount of members in a campaign from the Campaign Analytics subtab on the View Campaign summary page. You can filter the report data by lead or contact name and response date range.

Your application administrator can filter what user-defined or predefined campaign related reports to display to campaign users. For example, the default Campaign Analytics subtab search filter is Record Set = All Members. This search returns all campaign members with a status of Responded and Sent.