The meaning is roughly similar but they would be used differently. The first one would mean that many people have come into town, say, for the weekend. For example: "It's Friday night and there are many people in town."
The second has an ominous ring to it and would be used, for example, in: "I thought the bank in this small town would be a pushover, but there many people in the town
These are used differently. The first might be used, for example, in the following: "I had to be careful because there might be police around, but I was out of provisions. There was a town nearby and I decided to chance it. I went to the town to buy food."
The second is frequently heard. "A: Where have you been all day? B: I went to town."