A drab goalless draw with Scotland was sandwiched between 1-0 wins over Group D rivals Croatia and the Czech Republic.
Qualification into the round of 16 was already secured before Raheem Sterling’s header proved enough for victory over the Czechs at Wembley on Tuesday night.
Gareth Southgate’s side advance as pool winners as a result, despite having scored just twice in their three games.
The performances may not have been as eye-catching as some of the pre-tournament favourites but Henderson - who played his first 45 minutes of the finals having come on at half-time against the Czechs - believes England have plenty of reasons to be cheerful.
“It is very positive,” said the Liverpool captain.
“We have won the group. Our objective was to qualify, defensively we have looked solid with the clean sheets.
“We would like to have scored more goals, of course, but overall I think we have got to be pleased and look forward to the next round.
“When you get to the last 16 it is always going to be tough, always going to be a good team. We just need to be focused on ourselves, be ready and go out there and get a good result.”
Henderson was included in Southgate’s 26-man squad for the Euros despite not having featured for his club since February.
Southgate said it would be a “bonus” to be able to use the 31-year-old during the finals and his second-half display could yet see the midfielder start the round-of-16 fixture next week.
“I’m delighted to be back on the pitch, it has been a while,” he added.
“Delighted to be back, delighted to get three points and to win the group.”