Mike Edgerton, an owner of Universal Package Store in Groton, said he had about 20 customers in the first three hours, "which is not bad," he said.
A few customers were lined up at 10 a.m., he said.
Store owners, employees and customers will adjust to the seven-day-a-week availability of liquor, Edgerton said.
"I'm sure people will get used to it over time," he said.
Stephen Downes at CT Beverage Mart in Newington, said he was "kind of against" the legislation that Gov. Dannel P. Malloy signed into law on Monday. The legislature approved it earlier this month.
"I think we're going to do pretty well," Downes said.
A few people who "wanted to be first" were waiting for the doors to open Sunday morning and a "steady stream of visitors" came through the store on Sunday, he said.
Both businesses are adding staff for the extra day. Edgerton said his business will assess whether to stay open on Sundays in the winter. His business benefits from summer tourism, he said.
Downes said it remains to be seen if Sunday sales change consumer behavior. Customers typically consume alcohol the most on Thursdays, Fridays and Saturdays, he said.
Under the new law, Sunday sales will be allowed only from 10 a.m. to 5 p.m. at package stores. Supermarkets, which already sell beer, also will be able to sell beer on Sundays.
In addition to sales on Sundays, the new law also allows alcohol sales on Memorial Day, Independence Day and Labor Day and Mondays following any Independence Day, Christmas or New Year's Day that falls on a Sunday.
Package store owners fought legislative efforts for years allowing the Sunday sales. But this year, they reluctantly agreed because some had greater concerns with other parts of the bill, such as changes in pricing and other issues, urged by Malloy.
Those changes did not become law and will be taken up by a task force.
The state's Office of Fiscal Analysis says the Sunday sales could generate $5.2 million a year in revenue.
Lawmakers who represent districts that border Massachusetts and other states have said many of their constituents cross the border on Sundays to purchase alcohol.
Indiana is now the only state without Sunday retail sales of alcoholic beverages.