Officers were called to Hailstone Close on Saturday night where they found the partygoers.
The homeowner was handed a fixed penalty notice after they exceeded the number of people allowed to gather indoors by nearly seven fold.
Under the current rules, people can meet indoors in a group of up to six people or a group of any size from two households, while up to 30 people can meet outside.
A spokeswoman for West Midlands Police said: “We were called to a party on Hailstone Close, Rowley Regis on Saturday night.
“Around 40 people dispersed from the address on police arrival and the homeowner was issued with a fixed penalty notice.
“Despite the easing of restrictions, coronavirus is still here and continues to pose a significant risk to our communities.
“Please be responsible, exercise caution and do what you can to keep yourself and others safe.”
The spokeswoman said anyone unsure of the current restrictions should visit gov.uk/coronavirus.