How many of you? Have you considered parking at a SEPTA station and taking a train in? Market East station is really close to the historic district.

http://www.septa.org .

We're a family of 4 - Thanks for the link - I'll check it out.

No matter what route you take (I-76 goes all the way from Harrisburg to I-676 in Philly, from which you can exit on Fifth Street or Broad Street), listen to 1060 AM (KYW) for traffic reports. Have a road map to find an alternate route in case an overturned truck causes a 20 km backup on the Turnpike (Think it can't happen? Think again!) Be aware of the following terms:
The Schuykill (pronounced "skoo-kill") is I-76 from when it goes off from the Turnpike until it gets to the Delaware River. "Inbound" is east.
The Conshohocken Curve is Exit 332 on I-76.
The Blue Route is I-476 south from the Turnpike.
The Boulevard is US Highway 1.

Parking is a total ripoff in Center City. Either park at a Septa lot and ride mass transit all day (HIGHLY recommended to save time and aggravation) or get ready to pay $14 to park all day at a lot.

I can tell you that I have parked at the SEPTA station at Fort Washington (a ton of parking spots) and taken the R5 train into Center City a few times. It's right off the turnpike. There may be better options closer to Norristown, but I'm not familiar with them - and the Fort Washington Station is pretty easy to get to from the turnpike as I recall.

Are you returning home the same day, or staying overnight? If it's one day, taking Septa from Norristown is a good idea, but check out the cost.

http://www.septa.org/index.html

Clarification may help. If you consider a train ride, you would take Amtrak from HBG to 30th Street station in Philly where you could get a free transfer on a SEPTA (regional train) to Market Street East.I know it's not cheap but the train gives you great scenery (from Amish to heavily urban Philly) and a more relaxing ride.

Yeah, four people on Amtrak Harrisburg to Philly probably would not be cheap at all. Even Septa makes it not extremely cheap - maybe $5 per person or so each way. The reason to do it is to avoid the rush hour drive, because if you can do that and pay $20 to park for the day, you're a little ahead. I happen to love the train so I lean toward Septa.

Parking not really that high , was there last year parked in A public parking garage within a block of the district.
Sorry I can't give you an amount, but I remember I didn't complain about the price.