The borough hit the grim milestone over the weekend, less than a month after passing 3,000 cases.
The total now stands at 4,118 after 127 new cases were recorded over the weekend.
Scarborough is now averaging 50 cases per day as infection rates across North Yorkshire continue to rise.
The seven day infection rate per 100,000 people in Scarborough now stands at 320, its highest level since November 19.
The figure is below the average for England (517) but is above the average for the county (319).
Richmondshire has the highest rate in North Yorkshire at 411 cases per 100,000 people.
Mobile testing sites will be in Whitby, Scarborough and Filey this week for people with coronavirus symptoms to get tested.
To find your nearest test location visit www.northyorks.gov.uk/book-coronavirus-covid-19-test.
Scarborough’s walk-in coronavirus testing site at William Street Coach Park is offering testing seven days a week from 8am until 8pm. Appointments for all sites must be booked in advance.
Anyone who is showing coronavirus symptoms should register for a test on the NHS website at www.nhs.uk/conditions/coronavirus-covid-19/.
People who do not have access to the internet, or who have difficulty with the digital portals, can ring the 119 service to book.
Tests can be booked at https://www.gov.uk/get-coronavirus-test.