Irish immigrant Mary Mullen purchased 140 acres at $1.50 per acre from the US government near the southwestern edge of Watertown, Wisconsin. Mrs. Mullen—a widow—and her seven sons were the first of four generations to dedicate themselves to this land.

Frank R. Mullen Sr. opens a dairy and milk route in connection with his other farm interests southwest of town.  He supplies butter, milk and cream daily to a large number of customers in Watertown—and all say Frank’s butter, milk and cream are “the very best to be had.”

Seeking a better market for milk produced during the Great Depression, Frank Mullen, Sr. — along with sons Weber and Frank, Jr. — moved business operations from the family farm to 216 West Main Street in Watertown—what is now the Mullen’s Dairy Bar™ parking lot. Toward the end of the decade, a third brother Gerry joined the family business to round out the management team.

In the early 1940s, ice cream was first introduced to the Mullen’s Dairy™ menu. Initially, ice cream mix was supplied by the Pet Milk Company. With a surplus of cream available, Mullen's Dairy Bar™ began to produce their own ice cream mix. Next, an addition was built behind the building which marked a huge opportunity for the Mullen family. A bottle washing line was installed, separated from the “milk room” where pasteurization and bottling occurred.

Ready to expand their delivery operations, Weber Mullen spent $7,000 to acquire four Divco delivery trucks. Brother Gerry was the mechanic and spent many evenings rebuilding engines to ensure trucks were ready for next day’s deliveries. Post-war sparked an increase in route sales as soldiers came home and started families. Two additional Divco trucks were purchased to accommodate the increased number of households served.

​

​

​

Riding a wave of post-war growth, the 1950’s marked a heyday for Mullen's Dairy Bar™. Milk production received a tremendous upgrade when the family introduced a “Quick Time” Pasteurizer from Kusel Dairy Equipment. This investment revolutionized the way Mullen's milk was pasteurized and bottled. Instead of heating a 100-gallon tank of whole milk to 160 degrees and waiting for it to cool prior to bottling, the new pasteurizing technology allowed Mullen's to pump milk into one end—heat it up to 160 degrees and cool down for bottling – all within a matter of minutes. 

Finished milk was stored in small holding tanks which fed the bottle filling equipment. Perhaps the most notable improvement that came from this new technology: The Mullen boys could now take Saturdays off!

The 1950’s also included organizational changes for Mullen's Dairy Bar™. The three brothers eventually bought out their father Frank Sr. and went on to form their own partnership. This decade marked the end of the Mullen family farm when Frank Sr. sold the land after 111 years of faithful service.

After driving their delivery trucks for nearly 20 years, the Mullen family invested in a new line of Divco trucks—now with refrigeration—which meant block ice was no longer needed to keep the dairy products cold. This upgrade made the lives of Mullen's Dairy Bar™ delivery drivers easier as they could load up the trucks the night before and be ready to go early the next morning. 

​

​

​

After dedicating himself to the family business for more than 4 decades, Weber Mullen died unexpectedly from lung cancer in 1973. This had a profound effect on the family, as “Webb” handled most of the dairy’s business dealings. In honor of their brother’s legacy, brothers Gerry and Frank Jr. kept the dairy going with the help of family members and a dedicated team of employees.

​

​

​

In 1976, Weber’s son Bill along with his wife Karla purchased Mullen's Dairy Bar™ from uncles Gerry and Frank. Wanting to keep the family’s legacy intact, Bill and Karla continued to make investments in the dairy’s milk operations—eventually consolidating all raw milk purchases to six local farmers from the Watertown area. At this time, milk and ice cream were processed 3-4 days per week and Mullen’s Dairy was credited as one of the last Wisconsin dairies to use glass bottles for distributing their milk.

As supermarkets popped up across the landscape, a steady decline in milk delivery requests was observed. This shift in buying behavior resulted in Mullen's Dairy Bar™ ceasing operations of its bottling plant in favor of becoming a Golden Guernsey distributor. Mullen’s Dairy™ would be the last local dairy to provide home milk delivery until Howard “Pinky” Herold—a 35-year employee—made the last door-to-door milk delivery for Mullen’s in October 1979. Through the dedicated efforts of employees like chief ice cream maker George McFarland—Mullen's Dairy Bar™ continued to offer milk delivery service to Watertown area schools for a few more years.

With milk delivery a thing of the past, Bill and Karla Mullen began to usher in a new era for Mullen’s Dairy. In 1986, Mullen's Dairy Bar™ began offering hot food for the very first time—which would prove to be the perfect complement to their homemade ice cream recipes. As the ice cream business grew, additional investments were made in production equipment to keep up with demand. Now a popular regional destination, Mullen's Dairy Bar™ expanded in 1988 when Bill and Karla added a second location in Beaver Dam.

​

​

​

After being family owned and operated for the better part of a century, the Mullen family decided it was time to move on. In 1996, Ron and Gloria Luepke purchased the business and the building with the strict agreement that the Mullen's Dairy Bar™ legacy would be preserved. The Luepke’s were true to their word, going on to expand the eatery’s dining menu and winning several awards for Mullen's Dairy Bar™ ice cream. Like Bill and Karla Mullen, the Luepke’s were dedicated to their craft and worked together to build on the Mullen family legacy for many years. In 2006, after running the business for nearly a decade, the Luepke’s leased operations of Mullen’s Dairy Bar™ to a new management team who would run the business for approximately 10 years.

​

In 2016, Ron and Gloria Luepke announced they were selling Mullen’s Dairy Bar™ to three brothers from Oconomowoc: Josh, Matt, and Adam Keepman. The business would once again be run by a band of brothers—a family who like many from the area—developed a love for the Mullen's Dairy Bar™ legacy. Upon purchasing Mullen’s, the Keepman brothers made significant investments to the business including remodeling the kitchen and restaurant while also revamping the ice cream production facility. In 2018, for the first time in its 86-year history, Mullen’s Dairy Bar™ began offering its small batch homemade ice cream to retail outlets throughout Wisconsin. The Keepman's have also expanded Mullen's Dairy Bar to include scoop shops at The Boardwalk on Fowler Lake in Oconomowoc and The Smiley Barn in Delafield.