If you are a US citizen intending to travel to Croatia for not more than 90 days, you are not required to secure a visa. All you need is a valid passport covering the duration of your trip.
Upon arrival at Croatia, all foreign travelers are obliged to register at the local police. If you are staying at a private house, locate the nearest police station to register. But if you have hotel accommodations, registration will be taken care of by the hotel management. You may be charged a fine if you fail to register.
A temporary stay permit can be requested if there’s a need to stay in Croatia for more than 90 days. This should be applied for at the Croatian Embassy or Consulate in the United States.
Additional information regarding entry requirements are available through:
Embassy of the Republic of Croatia in the United States
2343 Massachusetts Avenue, NW
Washington DC, 20008-2803
Telephone: 00 1 202 588 5899
Fax: 00 1 202 588 8937